- what the weight of the body is, - to talk about the gravity force and distinguish it from the mass.
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Before the flight into space, the cosmonaut was put on a spring weight - it indicated 75 kg.
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)?
What will the same scale show, if we put on it a spaceman flying in a spaceship and being in a state of weightlessness?
Exercise 1
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Take a look at the figures and answer the questions:
a. What is presented in the following pictures? b. What physical quantity can be determined using the instruments shown in the pictures?
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a. We can use different types of scales. b. The scales measures body massbody massbody mass i.e. grams and kilograms.
Experiment
Experiment 1
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Research problem
Establishing the relationship between gravity force (measured as body weightbody weightbody weight) and mass of the body.
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.
No.
m [g]
m [kg]
Q [N]
1
2
3
4
5
2
3
4
5
6
7
8
Instruction
Attach the force meter to the tripod.
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).
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.
Calculate the mass of weights in kilograms, write the results in the third column.
Calculate the quotients, obtained by dividing the value of gravity force and the mass of the weights in kilograms. Round the results to an integer and write them in column 5.
Summary
After rounding the results to an integer, in the fifth column of the table in all rows you received the number of , we mark it with the symbol g.
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.
The number (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 body weight unit is newton [N], mass - kilogram [kg], whereas gravitational acceleration [], therefore:
The weight of the body is different on different planets and it depends on the gravity force on their surfaces.
Exercise 2
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Why the weight of the same man measured using the spring scale on the Earth, the Mars and the Moon are different?
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Conclusion
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The spring scalesspring scalesspring scales never directly measure the mass of bodies.
The spring scale measures the pressure force exerted on its weighing pan. This force is called the weight of the body.
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 planetplanetplanet. 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 massbody massbody mass as well as on the size of the planet (its radius).
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.
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Click on the tag and you will get the information.
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Summary
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:
Spring scalesspring scalesSpring scales never measure the weight of body directly.
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).
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 planetplanetplanet, depends either on the mass of the planet or the body massbody massbody mass, as well as on the size of the planet (the radius of the planet).
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.
Exercises
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Exercise 3
Exercise 4
Calculate the mass of the body hung on the dynamometer, which indicates the value of 75 N. The measurement is carried out on the surface of the Earth.
Exercise 5
Specify in English what conditions must be met to have a correct result of weight measurements.