Topicm17a00c88f5060e85_1528449000663_0Topic

Mass and weight of the body

Levelm17a00c88f5060e85_1528449084556_0Level

Second

Core curriculumm17a00c88f5060e85_1528449076687_0Core curriculum

II. Solving problems using physical laws and dependencies.

Timingm17a00c88f5060e85_1528449068082_0Timing

45 minutes

General learning objectivesm17a00c88f5060e85_1528449523725_0General learning objectives

Introduction to the notion of body weight.

Key competencesm17a00c88f5060e85_1528449552113_0Key competences

1. Identifying the gravity force.

2. Determining the difference between body weightbody weightbody weight and its mass.

3. Calculating the weight of the body near the Earth.

Operational (detailed) goalsm17a00c88f5060e85_1528450430307_0Operational (detailed) goals

The student:

- identifies the weight of the body,

- identifies the sources of various types of interactions based on the observed effects.

Methodsm17a00c88f5060e85_1528449534267_0Methods

1. Learning through observation.

Forms of workm17a00c88f5060e85_1528449514617_0Forms of work

1. Individual work.

2. Work with the whole class.

Lesson stages

Introductionm17a00c88f5060e85_1528450127855_0Introduction

Introductory questions.

Before the flight into space, the cosmonaut was put on a spring weight - it indicated 75 kg.

1. What would happen if he stood on the same weight, but on the surface of the Moon or Mars (skip the mass of the suit)?

2. What will the same scale show, if we put on it a spaceman flying in a spaceship and being in a state of weightlessness?

Task 1

Take a look at the figures and answer the questions:

[Illustration 1]

[Illustration 2]

[Illustration 3]

a) What is presented in the following pictures?

b) What physical quantity can be determined using the instruments shown in the pictures?

Conclusion:

a) We can use different types of scales.

b) The scales measures body massbody massbody mass i.e. grams and kilograms.

Procedurem17a00c88f5060e85_1528446435040_0Procedure

Experiment:

Research problem:

Establishing the relationship between gravity force (measured as body weightbody weightbody weight) and mass of the body.

Research hypothesis:

the weight of the body depends on the force with which the Earth

(planetplanetplanet) attracts the body and on the mass of the body.

You will need:

a) eight weights of 50 g each with hooks for hanging,

b) a force meter with an operating range up to 5 N,

c) tripod,

d) a piece of paper and a pen,

e) measurement table.

[Table 1]

Instruction:

1) Attach the force meter to the tripod.

2) Hang one weight on the force meter, read the indication on scales of the force meter and write the result in the measurement table (force in the fourth column, mass in column 2).

3) Add another weight, read the indication on the scales and write the result.

Repeat the third step until all of the weights are hanging on the force meter.

4) Calculate the mass of weights in kilograms, write the results in the third column.

5) Calculate the quotients, obtained by dividing the value of gravity force and the mass of the weights in kilograms, $\frac{Q}{m}\left[\frac{N}{kg}\right]$. Round the results to an integer and write them in column 5.

Conclusion:

1. After rounding the results to an integer, in the fifth column of the table in all rows you received the number of $10\frac{N}{kg}$, we mark it with the symbol g.

2. It means that the weight of the body is directly proportional to its mass. In other words; if the body massbody massbody mass doubles then the body weightbody weightbody weight also doubles.

3. The number $10\frac{N}{kg}$ (remember that is an approximate value) is the quantity characterizing the gravitational interaction of the Earth with the bodies located near its surface. It is called the acceleration of the gravity on the surface of Earth (acceleration due to the gravity) and letter g is its symbol. Thus, the formula for gravity can be written in the more general form:

And vice versa, knowing the weight of the body Q, we can calculate the mass of the body.

The weight unit is newton [N], mass - kilogram [kg], whereas gravitational acceleration [$\frac{N}{kg}$], therefore:

Task 2

Why the weight of the same man measured using the spring scale on the Earth, the Mars and the Moon are different?m17a00c88f5060e85_1527752263647_0Why the weight of the same man measured using the spring scale on the Earth, the Mars and the Moon are different?

[Illustration 4]

Conclusion:

1. Spring scales never directly measure the mass of bodies.
2. The scales are used for measuring the pressure force exerted on its weighing pan. This force is called the weight of the body.
3. The gravity force is the force with which the Earth (or another planet) attracts every body of any mass. Its sense is downward to the centre of the planet.
In relation to the body placed on the surface of the planet, the value of this force depends either on the mass of the planet or on the body mass as well as on the size of the planet (its radius).
4. The indications obtained on the same scales in the case of the same man were different on different planets, because the value of the gravity force is different. The body of the same mass transferred to Mars is attracted with less force by this planet than by the Earth and with an even weaker force by the Moon, if the body is transferred to the surface of the Moon.m17a00c88f5060e85_1527752256679_01. Spring scales never directly measure the mass of bodies.
2. The scales are used for measuring the pressure force exerted on its weighing pan. This force is called the weight of the body.
3. The gravity force is the force with which the Earth (or another planet) attracts every body of any mass. Its sense is downward to the centre of the planet.
In relation to the body placed on the surface of the planet, the value of this force depends either on the mass of the planet or on the body mass as well as on the size of the planet (its radius).
4. The indications obtained on the same scales in the case of the same man were different on different planets, because the value of the gravity force is different. The body of the same mass transferred to Mars is attracted with less force by this planet than by the Earth and with an even weaker force by the Moon, if the body is transferred to the surface of the Moon.

Task 3

Click on the tag and you will get the information.

[Interactive graphics]

Lesson summarym17a00c88f5060e85_1528450119332_0Lesson summary

1. During the lesson, we have learned about the relationship between body massbody massbody mass and gravity force. The formula for gravity can be written in more general form:

2. Spring scalesspring scalesSpring scales never measure the weight of body directly.

3. Spring scales measure the pressure forcepressure forcepressure force exerted on its weighing pan. This force is called the weight of the body. Correct weighing (mass determination by measuring the pressure force) requires motionless weighted body (to say it more precisely, only the movement that does not change the pressure on the pan surface is allowed).

4. The gravity force is the force with which the Earth (or another planet) attracts every body of any mass. The magnitude of this force exerted on the body placed on the surface of the planet, depends either on the mass of the planetplanetplanet or the body massbody massbody mass, as well as on the size of the planet (the radius of the planet).

5. The indications obtained on the same scales in the case of the same man were different on different planets, because the gravity force is different.

Selected words and expressions used in the lesson plan

body massbody massbody mass

body weightbody weightbody weight

gravity accelerationgravity accelerationgravity acceleration

leveled scalesleveled scalesleveled scales

planetplanetplanet

pressure forcepressure forcepressure force

scalarscalarscalar

spring scalesspring scalesspring scales