Page 9 - Spotlight A+ Physics Form 4.5

Form
4 Physics Chapter 3 Gravitation

5. Saturn, Uranus and Neptune have gravitational 8. The human body was created to live in a
acceleration almost equal to Earth’s gravitational acceleration of 9.81 m s . Thus,
–2
gravitational acceleration, g = 9.81 m s even the knowledge of the value gravitational
–2
though they have larger masses. However, their acceleration is important in space exploration
densities are lower than the Earth. and sustainability of life.
6. Mercury and Mars have lower gravitational 9. During space exploration far away from the
acceleration than the Earth due to their smaller Earth or near other planets, the body of an
masses. astronaut may be exposed to situations of low
or high gravity.
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Gravitational acceleration
https://bit.ly/2Vmdbyp Effect of gravity
https://go.nasa.gov/2ZbuzXF
7. The magnitude of the gravitational force that
acts on an object at the surface of the planet can 10. The effect of low or high gravity on human
be calculated when the value of gravitational growth are shown in the Table 3.2.
acceleration is known.
Table 3.2 Effect of change in gravity on human growth
CHAP Factor Effect of low gravity Effect of high gravity
3
(a) Change in density • Density of the body decreases. • Density of the body increases.
(b) Fragility of the • Bones become more fragile due to loss of • No significant change in fragility.
bones calcium.
(c) Size of the lungs • Increased or expanded. • Reduced or contracted.

(d) Blood circulation • Blood collects in the upper parts of the • Blood collects in the lower parts of the
system body. body due to difficulty to flow upwards.
(e) Blood pressure • Lower blood pressure and heart rate. • Higher blood pressure and heart rate.

Centripetal Force in the Motion of Satellites and Planets
1. Figure 3.7 shows three positions of a satellite Direction of
velocity
that orbits the Earth with a uniform speed.
2. An object in circular motion is continuously
experiencing change in its direction of motion
even though the speed is constant. Earth
3. When an object does circular motion, the
resultant force acting is always directed towards
the centre of the circle and is known as the Direction of
centripetal force. velocity

Centripetal force in the motion of
satellites and planets
https://bit.ly/2Vd3Uc1
Direction of
velocity
Figure 3.7 Satellite in circular motion

70 3.1.4 3.1.5