3) Dynamics

Question 1

What is a force?

Answer 1

A force is a push or pull upon an object resulting from the object’s interaction with another object.

Question 2

What are the two broad categories of force?

Answer 2

contact force and non-contact force.

Question 3

State one example of a contact force.

Answer 3

(Any one will do)
Frictional Force
Tension Force
Normal Force
Air Resistance Force
Applied Force

Question 4

State one example of a non-contact force.

Answer 4

(Any one will do)
Gravitational Force
Electrical Force
Magnetic Force

Question 5

When forces acting on an object is balanced, what it the resultant force?

Answer 5

F = 0 N

Question 6

When forces acting on an object is unbalanced, what it the resultant force?

Answer 6

F is not equal to 0 N

Question 7

What is a resultant force?

Answer 7

Resultant force is the product of the mass and the acceleration of the object and the direction of the force is the same as the object’s acceleration.

Question 8

What is the formula for resultant force?

Answer 8

F = ma

Question 9

Define weight. (on earth)

Answer 9

The weight of a body is the gravitational force exerted by Earth on the body.

Question 10

Define normal force.

Answer 10

The normal force is the force exerted by the contact surface on the body. It acts perpendicularly to the contact surface.

Question 11

Define tension.

Answer 11

The tension force is the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.

Question 12

Define friction.

Answer 12

Friction is a force that resists the motion of objects in contact with each other.

Question 13

Define air resistance. (also known as drag)

Answer 13

Air resistance is the force acting against an object moving through air.

Question 14

What is a free-body diagram?

Answer 14

A diagram which shows all the forces acting on a body.

Question 15

Define contact force.

Answer 15

The contact force is the force exerted by the contact surface on the body. It acts perpendicularly to the contact surface.

Question 16

State one method to reduce friction.

(There are more than 1 method)

Answer 16

1. Use lubricant.
2. Smoothen the surface.
3. Use rollers and ball bearings.
4. Separate surfaces by air cushion.

Question 17

State 2 factors that affect the size of friction.

Answer 17

1. the nature of surface (rough vs smooth)
2. the size of force pressing the surface together.

Question 18

Draw the free-body diagram of the box as it accelerates downwards.

Answer 18

(See how the contact force is now smaller than the weight.)

Question 19

Draw the free-body diagram of the box as it accelerates upwards.

Answer 19

(See how the contact force is now larger than the weight.)

Question 20

Draw the free-body diagram of the box as it remains stationary.

Answer 20

(See how the weight and contact force are of the same length which implies that both forces are equal.)

Question 21

What are the two methods of scale drawing to find the resultant force of two forces which are not parallel?

Answer 21

Parallelogram method and Tail to tip method.

Question 22

What is the relationship between the resultant force, F frictional force, F_f and applied force, F_a? (Refer to the diagram)

Answer 22

F = F_a - F_f