Body weight on a lever scale. Mass measurement (accurate weighing). Practice tasks and questions

The purpose of the work is to learn how to use lever scales and determine the mass of bodies with their help.

Equipment and materials: scales, weights, several small bodies different weights, jar, shot or dry clean sand.

Directions for use

1. Read the appendix to the work “Weighing Rules”.
2. Following the rules of weighing, measure the mass of several solids accurate to 0.1 g.

Additional task

There is a special weighing method called the taring method. When weighing using this method, an object whose mass they want to determine is placed on the left pan of the scale. A jar is placed on the right cup, in which pour dry sand or fine shot until until the scales come into balance. Then the object is removed from the left pan of the scale and weights are placed in its place and with their help the scales are brought into balance. The mass of these weights will be equal to the mass of the object. The taring method can be used to measure body weight quite accurately even on slightly out-of-tune scales.

Test this out. Place a pellet or a wad of paper on the left pan of the scale; this will upset the balance of the scale - the scale will go out of balance. Measure the masses of the bodies you have using the taring method and compare them with the result obtained when weighing on balanced scales.

Think and explain why the taring method can be used to measure body weight quite accurately even on slightly out-of-tune scales.

Weighing Rules

1. Before weighing, you must ensure that the scale is properly balanced. If necessary, to establish balance, you need to place strips of paper, cardboard, etc. on a lighter cup.
2. The body to be weighed is placed on the left pan of the scales, and the weights are placed on the right.
3. To avoid damage to the scales The body to be 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 scale.
5. Do not place wet, dirty, or hot bodies on the scales, pour powders without using a liner, or pour liquids.
6. Small weights should only be picked up with tweezers (Fig. 310).

Having placed the body to be weighed on the left pan, a weight having a mass slightly greater than the mass of the weighed body is placed on the right one ( selected by eye followed by inspection). 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 most important weight and so on until there is equilibrium has been 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.

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:

Devices and materials:

WEIGHING RULES

What physical quantity is determined using lever scales?

In what units is it measured (list all)?

_____________________________________________________________

Do the exercises:

8.4 t = ___________ kg 500 mg =____________ g

0.5 t = ___________ kg 120 mg = ____________ g

125 g = ___________ kg 60 mg = _____________ g

100 g + 20 g + 1 g 500 mg + 200 mg = ___________________________ g

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

Which scale pan is placed on:

body being weighed?____________________

weights?___________________________

PROGRESS

№ experience

Body name

Body weight, g

1

2

3

Conclusion:____________________________________________________________

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, weights, several small bodies of different masses.

WEIGHING RULES

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

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.

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

Small weights and weights should be picked up with tweezers.

Having placed the body to be weighed on the left cup, a weight having a mass close to the body weight (by eye) is placed on the right one.

If the weight pulls over the cup, then it is put back in the case; if not, it is left on the cup. Then weights of smaller mass are selected in the same way until equilibrium is achieved.

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

TRAINING TASKS AND QUESTIONS

What physical quantity is determined using lever scales? weight

In what units is it measured (list all)? In SI - kg, in l/r - g

Do the exercises:

8.4 t = 8400 kg 500 mg =0.5 g

0.5 t = 500 kg 120 mg = 0.12 g

125 g = 0.125 kg 60 mg = 0.06 g

100 g + 20 g + 1 g 500 mg + 200 mg = 121.7 g

20 g + 10 g +1 g + 200 mg + 100 mg = 31.3 g

Which scale pan is placed on:

body being weighed? left

weights? right

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

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

PROGRESS

Knowing the rules of weighing, measure the mass of several small bodies with an accuracy of 0.1 g.

Record the measurement results in the table:

№ experience

Body name

Weights with which the body was balanced

Body weight, g

1

2

3

Conclusion: the mass of the body is approximately equal to the sum of the masses of the weights balancing the scales.

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 should small weights and weights only be picked up 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.

Technological lesson map in physics in 7th grade.

Laboratory work No. 3 “Measuring body weight on lever scales.”

Structure and course of the lesson.

Application.

1. Motivational.

A challenge of ingenuity. The king ordered Archimedes to measure out as much gold as an elephant weighs. There were no such large scales anywhere. Archimedes had a raft at his disposal. How did Archimedes solve the problem?

Discussion. Formulate the topic and objectives of the lesson.

2. Studying new material.

1) Updating knowledge.

1) Fill in the gaps in the text.

Body weight is a physical ________ that characterizes its _______. How more mass body, the more ______ it is inert. To measure the mass of a body means to compare its mass with the mass of ____, made of an alloy of platinum and iridium, equal to _____.

Answer. Body weight is physical magnitude, characterizing it inertia. The greater the body weight, the more more inert. To measure the mass of a body means to compare its mass with the mass standard, made from an alloy of platinum and iridium, equal to 1 kg.

2) In ancient Babylon, a talent was taken as a unit of mass - the mass of water filling a vessel from which water flows evenly through a hole of a certain size over the course of an hour. What units of mass do you know?

Verbal counting. Convert the mass into the indicated units.

Answer.

2) Primary assimilation of new knowledge.

What methods of determining mass do you know?

Methods for determining body weight.
1) Weighing - measuring mass using scales.

2) Determination of mass by the interaction method.

Study the instructions “Weighing Rules” from the textbook “Physics. Grade 7”.

3) Initial check of understanding.

Laboratory work No. 3
“Measuring body weight on lever scales.”

Purpose of the work: learn to use lever scales and use them to determine body weight.

Equipment: scales with weights, a set of bodies of different masses.

Progress.

1.Knowing the rules of weighing, measure the mass of bodies with an accuracy of 0.1 g.

2. Write down the measurement results in a table.

3. Draw a conclusion.

4) Primary consolidation. Solve the problem.

To balance the body on lever scales, sets of weights were used, the mass of which is indicated in the table. What is the mass of each body?

5) Control of assimilation.

Check yourself!

1.What devices are shown in the picture?

2.What physical quantities can be measured with their help?

3.What rules must be followed when using them?

3. Reflection.

+I myself _______________________________________

? The hardest thing was _______________________

! I have an offer ___________________________