1. Revision Exercise 27 – Forces and its Related Concepts: Introduction
SECTION A:
1. C 2. C 3. B 4. D 5. D
6. A 7. C 8. B 9. C 10. D
11. C 12. B 13. D 14. D 15. A
SECTION B:
1. By pushing or pulling the ball.
2. pressure; mass; weight; force
3. N/m2; Pa
4. It can cause a moving object to speed up, slow down or stop immediately. It can
cause the moving object to move in a new direction.
5. Spring balance; weighing scale
SECTION C:
1. Although the screwdriver is heavier and thus, exerts a greater force, the surface
area in the line of force for the needle is much smaller. This results in a greater
pressure created by the needle than the screwdriver. The high pressure makes the
needle sharp.
2. The person exerts a force of 600 N. This force is countered by an equal upward
force exerted by the chair to the person sitting on it. Therefore, there is no
resultant force and the man stays in position.
Revision Exercise 28 - Forces and its Related Concepts: Friction
SECTION A:
1. D 2. A 3. D 4. A 5. C
6. B 7. D 8. A 9. D 10. A
11. C 12. D 13. D 14. B 15. C
SECTION B:
1. Water reduces the friction between the road and tyre surfaces.
2. For better traction; Rubber is a waterproof material.
3. Frictional force; contact; move
4. Frictional force; traction
5. Allow us to grip things and walk.
SECTION C:
1. Friction causes much wear and tear, and generates a lot of heat. These cause much
energy wastage. However, many life’s processes depend on friction and would be
impossible without it.
2. No, many life’s processes depend on friction. We will not be able to carry on with
our daily tasks, such as walking, without friction.

2. Revision Exercise 29 - Forces and its Related Concepts: Gravitational Force
SECTION A:
1. A 2. B 3. D 4. B 5. D
6. B 7. A 8. D 9. C 10. B
11. B 12. A 13. C 14. A 15. C
SECTION B:
1. Mass of the object and gravitational acceleration.
2. It helps to weigh down people and things.
3. It is a region in which a gravitational force can be experienced.
4. 120 N
SECTION C:
1. Although gravitational force between the chair and the table does exist, its effects
are not seen. The force is of a very small amount since the 2 masses are relatively
small.
2. Mass of the two objects in question and the distance that they are placed from
each other.
Revision Exercise 30 - Forces and its Related Concepts: Magnetic Force
SECTION A:
1. C 2. B 3. A 4. A 5. D
6. D 7. A 8. D 9. A 10. D
11. C 12. D 13. A 14. D 15. A
SECTION B:
1. (a) repel; attract (b) induction; electricity
2. Refrigerator
3. Coil a wire round any magnetic material. Then supply an electric current through
the wire.
4.
X
N
X
5. By heating it; hitting it against a wall.

3. SECTION C:
1. In alarm clocks, magnets are used in the alarm component. The beeping sound is
created by moving magnets. The doors of our refrigerators are held tightly shut by
magnets.
2. Electromagnets can be readily magnetized and demagnetised, depending on the
function required. Very strong electromagnets can easily be made.
Revision Exercise 31- Forces and its Related Concepts: Turning Effect
SECTION A:
1. B 2. B 3. B 4. D 5. D
6. B 7. B 8. D 9. C 10. B
11. B 12. A 13. A 14. B 15. A
SECTION B:
1. Pivot and fulcrum.
2. moment and torque
3. The moment of a force is defined as the product of the force and the perpendicular
distance from the line of action to the pivot.
4. The line of action of the force is the direction in which the force acts towards, in a
particular motion.
5. A pivoted object of mass rotates around its pivot due to a force acting on it.
SECTION C:
1. Clockwise
2. Equal. A perpendicular force of 100 N acts 10 m away from a pivot. The moment
of the force is 1000 Nm.