How to weigh on a lever scale. Following the rules of weighing, measure the mass of several solids. Main types of educational activities of students

Laboratory work No. 3 page 161

Goal of the work: learn to use lever scales and use them to determine the mass of bodies.

Devices and materials: scales with weights, several small bodies of different masses.

Weighing – a method of measuring mass using scales.

Other units of mass:

1 t = 1000 kg

1 c = 100 kg

1 g = 0.001 kg

1 mg = 0.000 001 kg

Safety regulations.

1.Be careful with scales. Follow the weighing rules.

2. There should be no foreign objects on the table.

3. Place the scale in the middle of the table.

4. Do not lose weights and weights, especially do not put them in your mouth!!!

I have read the rules. I undertake to fulfill . ______________________

/Student's signature/

Weighing rules.

• Before weighing, make sure that the scales are balanced. If necessary, to establish balance, you need to place strips of paper, cardboard, etc. on the lighter pan of the scale.
• The body to be weighed is placed on the left pan of the scales, and the weights are placed on the right

Weighing rules.

3. To avoid damage to the scales, the body being weighed and the weights must be lowered onto the cups carefully, without dropping them even from a small height.

4. You cannot weigh bodies heavier than the maximum load indicated on the scales. (200g.)

Weighing rules.

5. Do not place wet, dirty, hot bodies on the scales, pour powders without using a liner, or pour liquids.

6. Small weights should only be picked up with tweezers.

Weighing rules.

7. Having placed the body to be weighed on the left pan, a weight having a mass slightly greater than the mass of the body being weighed is placed on the right pan (selected by eye and then checked). If this rule is not followed, it often happens that there are not enough small weights and you have to start weighing all over again. If the weight pulls over the cup, then it is put back into the case, but if it doesn’t, it is left on the cup. Then the same is done with the next weight of smaller mass, etc., until equilibrium is achieved.

Having balanced the body, calculate the total mass of the weights lying on the scale. Then the weights are transferred from the scale pan to the case.

Check that all the weights are placed in the case and that each of them is in its intended place.

Training tasks and questions

• What physical quantity is determined using lever scales? ____________________

2. In what units is it measured (name all)?

________________________________

3.Do the exercises:

8.4 t = _______ kg

0.5 t =________ kg

125 t =________ kg

500 mg = ________ g

120 mg =_________ g

60 mg = _________ g

4.100 g +20 g + 2 g + 1 g +500 mg + 200 mg =___g

20 g + 10 g + 1 g +200 mg + 100 mg =_________g

5.Which cup is it placed on?

body being weighed? on ____________

weights? on ________________

6.What needs to be done on a lever scale before weighing?_____________

Progress.

1. Following the rules of weighing, measure the mass of several solids to the nearest 0.1 g.

Progress.

2. Record the measurement results in the table.

№ experience

Body name

Body mass

m , G

Cube

Body mass

m , kg

Body weight on electric scales m , G

Conclusion:

I learned to use lever scales and with their help measure the mass of various bodies with an accuracy of .......

Additional task.

• Which weights from the school set must be placed on a cup of educational scales in order to balance a piece of sugar weighing 10.50 g lying on another cup? (set of weights: 10g, 5g, 5g, 20mg, 20mg, 10mg).
• Express the mass of bodies in kilograms: 3.5t; 0.25t; 150g; 15
• How many grams are in 7.5 kg?
• The mass is designated by the letter ……….
• 100g + 20g + 2g + 1g + 500mg + 200mg =…..

Homework

§19, 20

Exercise No. 6 (1, 2, 3)

The purpose of the lesson: teach students to use lever scales and use them to determine body weight.

I. Checking the assimilation of the studied material.

1) Frontal survey:

1. What property of bodies did you learn about in the previous lesson?
2. How does the inertia of bodies manifest itself?
3. What physical quantity characterizes the inertia of bodies?
4. Which of the two interacting bodies is more (less) inert?
5. What is the basic unit of mass in the SI system?
6. What derived units of mass do you know?

2) Convert to SI:

1. 200 g = ? (0.2 kg)
2. 4500 mg = ? (0.0045 kg)
3. 0.5 t = ? (500 kg)
4. 3.5 c = ? (350 kg)
5. 2500 g = ? (2.5 kg)
6. 0.07 t = ? (70 kg)
7. 20 c = ? (2000 kg)

3) Solve problems:

1. The weight was lowered into a vessel with water. Has the mass of the weight changed?
2. The air under the pump piston was compressed. Has the mass of air changed?
3. Does the mass of a substance change when water turns into ice or steam?

II. Learning new material.

What methods of determining mass do you know?

Fastening: Calculate the mass of cart No. 2 if its speed module is 4 times greater than the speed module of cart No. 1.

What types of scales do you know?

Study the structure and principle of operation of lever scales (working with the textbook by A.V. Peryshkin “Physics 7th grade” p. 47).

What is the main part of the scale?

What is the condition for equilibrium of the scales?

How to determine body weight using scales?

What rules should be followed when determining body weight?

Weighing rules:

1. Balance the scales using strips of paper, cardboard, etc.
2. Place the body to be weighed on the left side of the scale and the weights on the right side.
3. Having balanced the body, calculate the total mass of the weights lying on the scale.

Review a set of weights and weights for a laboratory scale and answer the questions.

1. Why are there identical ones in a set of weights?
2. Why is it advisable to start weighing with a larger weight?
3. Why small weights And should the weights be taken only with tweezers?
4. Why are there no weights of 30 g, 3 g and weights of 300 mg, 30 mg in the set?
5. What can replace 4 g, 40 g weights and 400 mg, 40 mg weights?

III. Performing laboratory work.

Progress.

1) Read the weighing rules carefully.

2) Adhering to the rules, measure the mass of the bodies given to you.

3) Write down the measurement results in the table.

4) Individual tasks.

Option 1. Measure the mass of sand in the box.

Option 2. Measure the mass of liquid in the glass.

5) Write down the conclusion: what you measured and what you learned.

IV. Homework.

Suggest and describe a method for determining the mass of one drop of water using a laboratory balance.

Physics lesson in 7th grade on the topic "Measuring body weight on lever scales"

Lesson objectives: developing the ability to compare the masses of two bodies, measure body weight on lever scales, express thoughts and describe actions in oral and written speech.

I have six servants,
Agile, daring.
And all that I see around is
I know everything from them.
They are at my sign
Are in need.
Their names are: How and Why,
Who, What, When and Where.
R. Kipling (translation by S.Ya. Marshak)

1. Organizing time.
2. Updating the topic.

In the last lesson we got acquainted with the physical quantity - body mass.

What property of a body is characterized by mass? (Inertia).

How does the inertia of bodies manifest itself? (The less the speed of a body changes during interaction, the more inert it is).

What is the basic unit of mass? (kg).

Lesson topic: “Measuring body weight on lever scales.” Lesson goal: learn to measure body weight.

IV. Justification of the relevance of the topic.

Why do you need to measure body weight? To answer this question, we conducted a study, which we presented in the form of a presentation. Student performances:

Find out which professions people need to measure body weight.

What scales do they use to do this?

Collect Interesting Facts body mass measurements.

To complete the task, we split into groups.

The first group will study literature. The guys in this group must find interesting facts related to mass.

The second group will go to shops and other retail outlets.

The third group will find out in the hospital and clinic what importance measuring body weight has for the doctor and his patient.

The guys from the fourth group will visit the post office and find out how accurately parcels and parcels are weighed at the post office.

At the clinic we visited the office of a healthy child.

Monthly weighing of children from birth to one year allows doctors to conclude whether the baby is healthy and whether he is developing correctly.

There are scales for adults in the clinic and hospital. We found them at the endocrinologist and in the emergency room. People who are overweight are more likely to suffer from some disease.

In the Soyuz store we carefully examined the scales. We found out that they were manufactured in 1999. We made a test purchase. In the Visit store we saw more modern and convenient scales.

At the post office, scales are necessary for weighing parcels, parcels, and registered letters. If a postal worker does not correctly measure the weight of a parcel, then he may get into trouble later.

We concluded:

• Body weight measurement, important point for specialists of many professions.

Teacher: Measuring body weight is a very important point in physics lessons.

"Measuring body weight on lever scales."

Goal of the work– learn to use lever scales and use them to determine the mass of bodies.

Devices and materials: scales with weights, several small bodies of different masses.

Directions for use

1. Read the weighing rules carefully.
2. Adhering to the rules, measure the mass of the bodies given to you.
3. Record the measurement results in the table.

VIII. Individual task.

Task No. 1

Measure the mass of sand in the box.

Task No. 2

Measure the mass of liquid in the vial

IX. The discussion of the results. Summarizing.

X. Homework.

Interview your mother or grandmother: In what situations at home do you have to measure the mass of bodies, how do they do it?

Goal of the work: learn to use lever scales and measure the mass of bodies with them.
Devices and materials: scales, weights, weighed bodies of different masses.
Work order:

1. Learn the rules for weighing on lever scales:
a) before weighing it is necessary to balance the scales;
b) the body to be weighed is placed on the left pan of the scales, and the weights are placed on the right (vice versa for left-handers);
c) the body to be weighed and the weights are placed on the cup carefully so as not to damage the scales;
d) liquid, loose, hot bodies must be placed on the scales so as not to stain them;
e) the mass of weighed bodies should not exceed maximum weight, for which the scales are designed;
f) small weights should be taken with tweezers, large ones with a piece of paper, so as not to change their mass;
g) they begin to balance the weighed body with weights greater mass, then smaller ones, otherwise there may not be enough small weights.

1. Measure the mass of several solids.
2. Determine the absolute measurement error of the scales.
3. Record the measurement results in Table 19, taking into account the measurement error.

5.* Additional task. Come up with and plan an experiment to weigh a liquid.
1) weigh the vessel;
2) pour liquid into it;
3) balance the scales and obtain the mass of liquid and the mass of container;
4) subtract the mass of the vessel from the total mass.

Measure the mass of the liquid and record the measurement result.
m (together) = 120 g.
m (packages) = 12 g.
m (liquid) = 120-12 = 108 g.

92. Experimental task. Measure the mass of one drop of water using a bottle of water, a pipette, a scale, a weight, or a vessel.
1. Measure the mass of the empty container— mс
2. Using a pipette, drop 50 drops of water into an empty container and weigh it. This way you will find the mass of the vessel and water– mc+v.
3. Determine the mass of 50 drops of water: mв=mc+в – mc.
85 g-15 g =70 g
4. Calculate the mass of 1 drop of water: mк =

70:50 = 1.4 g.
5. Repeat the experiment by pouring 100 drops of water into an empty vessel. Record the results of measurements and calculations in table 20.

Conclusion: errors were made and the results did not match.

What should I do to measure the mass of a drop of water more accurately?
It is necessary to reduce the number of drops and calculate their average mass.

Experimentally test your hypothesis about the accuracy of measuring the mass of a drop of water. Write down the results.
They added 6 drops, then 6 more, and averaged the result.
m = 2.4 g.

Laboratory work “Measurement of mass, volume and density of the body”

Measuring body mass, volume and density.

Goal of the work: learn to use lever scales and their help to determine the mass of bodies, determine the volume of a solid body using a ruler and find the density of homogeneous bodies of regular shape.

Devices and materials: scales with weights, a ruler, several small homogeneous bodies of regular shape of different masses.

• The body to be weighed and the weights must be lowered onto the cups carefully, without dropping them.

1. Following the rules of weighing, measure the mass of solids to the nearest 0.1 g.
2. Record the measurement results in the table.
3. Using a ruler, measure the length, width and height of solids of the correct shape, write the measurement results in the table (length a, height b, width c).
4. Calculate the volume of the block using the formula:

5. Using the formula for calculating density, calculate the density of the solid:

xn--j1ahfl.xn--p1ai

Laboratory work “Measuring body weight on lever scales”

Laboratory work " Measuring body weight on lever scales."

“Laboratory work “Measuring body weight on lever scales””

Laboratory work 0.1.

Measuring body weight on a lever scale

Goal of the work: learn to use lever scales and use them to determine the mass of bodies.

Equipment: scales with weights, several bodies of different masses.

Following the rules of weighing, measure the mass of several solids to the nearest 0.1 g.

Record the measurement results in the table.

Write down your conclusion about the work done.

Before weighing, make sure that the scales are balanced.

The body to be weighed is placed on the left pan of the scale, and the weights are placed on the right.

To avoid damage to the scales, the body being weighed and the weights must be lowered onto the cups carefully, without dropping them even from a small height.

You cannot weigh bodies heavier than the maximum load indicated on the scale.

Small weights should only be picked up with tweezers.

Having placed the body to be weighed on the left pan, a weight having a mass slightly greater than the mass of the body being weighed is placed on the right pan. If this rule is not followed, it often happens that there are not enough small weights and you have to start weighing all over again.

If the weight overtightens the cup, then it is put back in the case, but if it doesn’t overtighten, it is left on the cup. Then the same is done with the next weight of smaller mass until equilibrium is achieved.

Having balanced the body, calculate the total mass of the weights lying on the scale. Then the weights are transferred from the scale pan to the case.

Check that all the weights are placed in the case and that each of them is in its intended place.

Laboratory work: constructing lever scales and measuring mass with these scales

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Lab: Measuring body weight on a lever scale

Purpose of work: to study the structure of lever scales, a set of weights and

practice techniques for using them and using them to determine the mass of bodies.

Equipment: scales with weights, wooden block, 100 g weight, plastic body (1 pc.).

The work is of great practical importance, since its implementation develops techniques for handling one of the most common measuring instruments - lever scales. Students will need the acquired weighing skills not only to perform other laboratory work, but also in everyday life.

First, students examine a set of weights and determine its composition, quantity

weights, the mass of which is indicated in grams, the number of milligram weights, the order of placement of weights and tweezers in the stack. They learn that weights and weights are transferred to the scales with tweezers, which are held in the hand with their curved ends up.

Then they get acquainted with the scales. Hang them on a tripod and balance them. To save small weights, balance is achieved with pieces of paper. The scales are considered balanced if their pointer is in a strictly vertical position.

The first thing to determine is the mass of the load. Here the students are explained that the body being weighed is placed on the left pan of the scales, and the weights are placed on the right.

Weighing begins using heavy weights. First, a weight of the greatest mass at which the body still outweighs is placed on the scales. Then they add a smaller one, but one in which the body still outweighs. Smaller weights are added one at a time until the scales are balanced. The mass of a body is determined by the sum of the masses of all the weights that went into balancing it. Having determined the body weight, the weights are returned to the stack with tweezers.

Weighing rules are reinforced by asking students to measure the mass of a metal bar.

You cannot weigh bodies heavier than the maximum load indicated on the scale.

Do not place wet, dirty, or flammable bodies on the scales, pour powders without using a liner, or pour liquids.

Having placed the body to be weighed on the left cup, a weight is placed on the right one. If the weight overtightens the cup, then it is put back into the case, but if it doesn’t overtighten, it is left in the cup. Then I do the same with the next weight, a smaller one, etc., until balance is achieved.

Following the rules of weighing, measure the mass of several solids with an accuracy of 0.1 g.

Laboratory work No. 3 in physics, grade 7

Laboratory work No. 3.

Goal of the work

View document contents
“Laboratory work No. 3 in physics, grade 7”

Laboratory work No. 3.

Measuring body weight on lever scales.

Goal of the work: learn to use lever scales and use them to determine the mass of bodies.

Devices and materials: scales with weights, several small bodies of different masses.

Before weighing, make sure that the scales are balanced. If necessary, strips of paper should be placed on a lighter cup to establish balance.

Do not place wet, dirty, or hot bodies on the scales, pour powders without using a liner, or pour liquids.

Having placed the body to be weighed on the left pan, a weight having a mass slightly greater than the mass of the body being weighed is placed on the right pan.

If the weight pulls the cup, then it is put back in the case, but if it doesn’t, it is left on the cup. Then the same is done with the next weight of smaller mass.

Having balanced the body, calculate the total mass of the weights lying on the scale.

Then the weights are transferred and placed in a case.

Using weighing rules, measure the mass of several solids to the nearest 0.1 g.

The purpose of the laboratory work is to study the technique of using lever-type scales and master practical skills in measuring mass. The operating principle and design of lever scales allow you to perform weighing with sufficient accuracy. The simple and reliable device is based on the use of an equal-arm lever. People have used such a reliable device for thousands of years.

Preparatory stage and weighing process with a balanced device

Before measuring body weight on a lever scale, it must be balanced. As a result of the balancing procedure, it is necessary to ensure that the instrument needle matches the central mark as accurately as possible. To fine-tune the measuring device, you can use pieces of cardboard - they are added to the pan of the scale that turns out to be lighter.

Important. The weighing process involves balancing the object being weighed with other bodies (weights), the mass of which is indicated on their surface.

When equilibrium occurs, the weight of the body under study and the sum of the masses of the weights will coincide in size. Now it remains to compare the masses of bodies that are placed on one and the other pan of the scale. Thus, after calculating the total mass of all weights, you can find out the mass of the body being weighed.

Weighing by taring on detuned scales

Taring is a special weighing method. To use it, you should use, in addition to weights, a jar and shot (dry sand). On one cup at the initial moment of measurement there will be a body (object) that needs to be weighed. A jar is placed on the second to level the mass with the object, into which shot and (or) dry sand are added.

After balance is achieved, the object being measured is removed and weights are placed in its place, the selection of which also achieves balance. The masses of the object and weights are equal.

The advantage of using the tare method is the possibility of fairly accurate weighing on detuned scales. How accurate this method is can be judged by the fact that after achieving equilibrium, adding even a small piece of cardboard to one or another scale will lead to an imbalance in the balanced system of scales. It can be recommended to check the accuracy of measurement readings using lever-type scales in one and the second way.

Weighing Rules

There are a number of rules that, if followed, will allow you to measure body weight on a scale with the required accuracy.

It is important to properly balance the measuring device - it must be placed on a rigid and level base area. It is advisable to place the weights on the scale on the right, and the object being measured (the body) on the left.

Placement of weights and measured bodies should be done with care, avoiding falls and impacts. It should be borne in mind that among the characteristics of this type of measuring instruments, an important indicator is the maximum load.

When weighing, you should not place objects (bodies) on the scales whose weight exceeds the maximum permissible value of the indicator. Heavy bodies should be weighed using instruments with appropriate characteristics.

It is highly undesirable to place hot, dirty or wet objects on the scale. You should not pour any liquids or place bulk substances. If it is necessary to measure their mass, you can use one or another container with a known net mass. Care during the weighing process will increase the service life of the scale.

Important. In accordance with the rules, tweezers should be used if you need to use small weights or lighter weights.

They work with weights as follows:

1. A weight is placed on the right cup, the weight of which is greater than the object being weighed placed on the left cup. After making sure that she is pulling the left cup with the object, they put it in the case.
2. They take the next one at par. If it is less than the mass of the object being weighed, we leave it in the cup.
3. The next weight or weight is selected in exactly the same way. If you follow a similar algorithm, you will always have enough small weights for weighing.
4. Each weight in the case has its own place, after completion of the measuring process - they should all be in their places.

To fully assimilate the information material, it is worth consolidating it in practice. Take any metal block whose weight does not exceed the permissible measurement limit, or other objects and try to measure their mass as accurately as possible. Write down the result obtained, for example, in the form: 20g + 10g + 2g + 1g + 500mg + 10mg = 33.51 g.

Conclusion

Body weight, when measured with lever-type scales, can be determined with great accuracy.

Tare scales

In addition to manual scales, tare scales VKT-1000, T-1000, as well as tabletop ordinary scales (NO) are used in the pharmaceutical production of medicines.

Tare scales VKT-1000, T-1000 are general-purpose scales of class II, which are used for weighing liquid, viscous and granular substances. Their designs are not fundamentally different from manual scales. These are also lever scales with a straight equal-armed beam, but with a larger load capacity. An equal-arm rocker with one support and two load-receiving prisms rests on a cushion located on the column. Earrings with removable cup holders and cups are suspended from the points of the weight-receiving prisms. Balance regulators are located at the ends of the rocker arm. The arrow is rigidly attached to the rocker arm and the reading scale. The scales are installed plumb.

Manual scales

In pharmacy practice, manual scales of the BP and VSM brands are used to weigh small quantities of medicines. The industry produces hand scales of 4 standard sizes (Table 1).

Brands and sizes of hand scales

Weighing on hand scales

Hand scales are used almost exclusively for weighing bulk solids in quantities from 0.05 to 100 g.

1. When not in use, hand scales are kept on the hook of a special tripod, or less often in a closed box. When placing the scales on the tripod hook, place one cup of the scales in another cup and hang the scales by the cords of the lower cup so that the tripod hook passes between the vertically hanging beam and the cords of the lower cup. To avoid unnecessary wear of the prism tips, do not hang the scales by the ring of the holder.

2. Before starting work, make sure that the scales are balanced: the swing of the rocker is stopped not by pinching the arrow inside the holder, but by placing the horizontal palm of the right hand under the cups or lowering it until the bottoms touch the table surface.

3. When weighing on hand scales, they are held suspended in the left hand. It is usually recommended to grasp the scales with the thumb and forefinger of your left hand so that the holder hangs strictly vertically and is completely free. The middle and ring fingers of the left hand are placed on both sides of the holder, without touching it, but having the ability to limit the movement of the scale arrow and, if necessary, stop its vibrations. Before weighing, place a sheet of white paper under the right pan of the scale.

4. Having made sure that the scales are balanced and their cups are clean, the required amount of weights is placed on the left cup, and the substance to be weighed is placed on the right cup (small weights are taken only with tweezers, protecting the laces of the scales from contamination with powder). Nameless or thumb with the left hand they support the arrow of the scales, not allowing it to deviate far to the left from the plane of the frame and feel the approach of equilibrium. At the end of weighing, wipe the scale cups with a gauze cloth.

5. To weigh out toxic substances, use a separate weight.

Weighing on tare scales

Tare scales are used for weighing bulk, liquid and viscous substances in quantities allowed by maximum loads (from 50 g to 1 kg). Before starting work, you should install the scales plumb and balance the scale cups (using the balance regulators); the arrow should be at zero or deviate from it by equal distances. It is recommended to place weights and weights in the middle of the cups. The total mass of the weights is calculated carefully, preferably twice - when placing them on the scale and when removing them from it. Weighing of bulk substances is carried out directly into a paper bag or box with an appropriate label, sometimes onto a sheet of writing, paraffin or parchment paper. The prepared package, opened, is placed on the right pan of the scale. The same bag or sheet of paper and weights are placed on the left cup as a container. From a rod that is held in right hand, a powdery substance is carefully poured into the bag, and the rod is slightly rocked along the longitudinal axis; Lightly tap the neck of the rod with the index finger of the right hand. Touching the cup with the weight with the index finger of your left hand, try to feel the moment of balance.

Caring for scales and weights

1. Before starting weighing, check the condition of the scales, brush off the dust from the cups and set the zero point (see below).

2. The object to be weighed and the weights can be placed on and removed from the scales only when the lock is closed, i.e. when the arrester is lowered. When the guard is open, do not touch the scale. The locking disc should be turned slowly, smoothly and carefully.

3. The scales must not be moved from their position.

4. The scale should not be overloaded beyond the permissible limit (100 g), as this may lead to damage to the scale. In case of doubt, the object must be weighed on a laboratory chemical balance and, after making sure that its mass does not exceed the limit, proceed to weighing it on an analytical balance.

5. Do not place wet or dirty objects on the scales. Do not spill or spill anything inside the scale cabinet. Do not weigh hot objects or very cold ones. The item being weighed must be at the temperature of the room in which the scale is located.

6. Do not place the substance to be weighed directly on the scale pan. You cannot weigh on a sheet of paper. Weighings are carried out on a watch glass, in a weighing bottle, in a crucible or in a small glass. Hygroscopic substances, as well as liquids that emit caustic vapors, are weighed in a closed weighing bottle.

7. When weighing, it is allowed to use only the side doors of the scale cabinet; the front wall of the cabinet must be closed.

8. When weighing, weights should be handled only with tweezers. The weights can only be on the scale or in a case in its own nest.

9. When not in use, the scales must always be locked (the lock is lowered). You cannot lean your elbows on the table on which the scales stand or disturb the person working on the scales with extraneous conversations. In case of any malfunction of the scales, you must contact your supervisor.