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Force, Gravity and Space-time
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Worksheet 1 How do objects fall?
Time to Think (p. 6)
1.
People tended to accept the ideas or wisdom of the authority without question.
2.
(a) No satisfactory result could be predicted.
(b) The combined masses would fall at the same speed.
3.
Release a heavy mass and a light mass of the same material from the same
height and find whether the heavier mass will reach the ground faster than the
lighter mass.
Time to Think (p. 8)
4.
The objective of the experiment is to find out whether the idea of Aristotle or
Galileo is correct.
5.
They watched which ball reached the ground first, and the position of the
slower ball when the first ball reached the ground.
6.
The result supported Galileo’s idea because both masses fell at the same speed
as they reached the ground almost at the same time.
7.
According to Aristotle, when a 100-pound ball reaches the ground, the 1-pound
ball should have fallen for about 1/100 of the height. This means that if the total
height is 100 cubits, the small ball should be about 99 cubits above the ground
when the large ball reaches the ground. So the experimental error is about 99
cubits. But according Galileo, the experimental error is only 2 inches.
8.
Galileo used inclined planes to slow down the fall of the balls.
9.
The pulse of a person may vary from time to time and may be affected by
factors such as emotion and physical activities of the person.
10.
d = kt2 (or k = d/t2) where k is a constant.
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Force, Gravity and Space-time
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Worksheet 2 Understanding the motion of bodies on the Earth and in space
Time to Think (p. 15)
1.
When Newton saw an apple fall from a tree, he wondered whether the force
which pulled the apple to the ground was the same force which held the Moon
in its orbit around the Earth.
2.
(a) A force called gravity acts on the stone by the Earth, causing it to fall faster
and faster.
(b) The Earth exerts an attractive force (the gravity) on the Moon, keeping the
Moon in its orbit.
3.
Both of the motions of a falling stone and the Moon are under the influence of
gravity of the Earth.
4.
This force exists between any two bodies with mass, no matter whether they are
earthly or celestial bodies.
5.
(a) The distance between the Equator and the centre of the Earth is greater
than that between the North Pole and the centre of the Earth. The greater
the distance between two bodies, the smaller is the gravity between them.
(b) The mass of the Earth is about 100 times that of the Moon, and the radius of
the Earth is about 4 times that of the Moon. Thus the gravity of the Earth is
about 100/42 ≈ 6 times that of the Moon. Thus the gravity between the
Moon and the person will be 1/6 of that between the Earth and the person.
6.
He meant that his success had been based and built on the achievements of
previous scientists.
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Force, Gravity and Space-time
Answers
Worksheet 3 The greatest scientist in the 20th century
Time to Think (p. 21)
1.
Einstein worked in the field of theoretical physics, with mathematics as the
instrument.
2.
Nuclear power is the energy generated from the destruction of matter during
nuclear reactions. This is not a kind of renewable energy.
3.
People at that time firmly believed that light is a kind of wave.
4.
Einstein used the kinetic theory to explain Brownian motion. To test his
explanation, a microscope with very high power of magnification should be
used to measure the rate of drifting of a suspended particle during Brownian
motion.
5.
One prediction is that when light from a distant star passes close to a large
mass, such as the Sun, it will be deflected by a very small amount. This
prediction is difficult to test because the Sun is so bright that a slight deflection
of light caused by its gravity cannot be detected.
6.
The observations only give support to, but cannot confirm, Einstein’s theory.
7.
A possible conclusion is that Einstein’s general theory of relativity is wrong or
needs to be modified.
8.
The true scientific attitude is that a theory would be unacceptable if it fails in
certain tests.
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