TOPIC 4: FORCES

Question 1

[Definition] Field of force

Answer 1

A region of space where a particle experiences a force

Question 2

[Definition] Gravitational field

Answer 2

A region of space in which a gravitational force acts on a mass

Question 3

[Definition] Electric field

Answer 3

A region of space in which an electric force acts on a stationary charge

Question 4

[Definition] Magnetic field

Answer 4

A region of space in which a magnetic force acts on a current-carrying conductor, moving charge, or a permanent magnet

Question 5

[Definition] Centre of gravity

Answer 5

The point where all the weight of a body seems to act on

Question 6

Free body diagram VS Labelled force diagram

Answer 6

Labelled force diagram requires specific labelling of ALL forces (e.g. normal contact force by table on mass)

Question 7

Main forces in the chapter

Answer 7

1. Normal contact force
2. Weight
3. Friction
4. Lift / Upthrust
5. Tension & Compression
6. CONTACT/REACTION FORCE (NOT NCF !!!)
   - It is the vector sum of ALL the forces at the contact surfaces

Question 8

[Definition] Hooke’s Law

Answer 8

Hooke’s law states that the change in length of a material is directly proportional to the force applied on it, provided that the limit of proportionality is not exceeded.

Question 9

[Formula] Hooke’s Law

Answer 9

F = kx

F: Force applied (N)
k: Proportionality constant (Nm^-1)
x: Change in length (m)

Question 10

[Definition] Elastic limit

Answer 10

The point beyond which the spring does not return to its original length when the force is removed

Question 11

[Definition] Pressure

Answer 11

Pressure is defined as the force per unit area.

Question 12

[Formula] Pressure

Answer 12

p = F/A
p = hpg

Question 13

What is upthrust equals to?

Answer 13

Weight of fluid displaced

Question 14

Condition for translational equilibrium

Answer 14

No resultant force

Question 15

Condition for rotational equilibrium

Answer 15

No resultant torque about any point

Question 16

[Definition] Principle of moments

Answer 16

Principle of moments states that for a body in rotational equilibrium, the sum of the clockwise moments about any point is equals to the sum of anti-clockwise moments about the same point

Question 17

[Definition] Moment of a force

Answer 17

Moment of a force about a point is the product of the force and its perpendicular distance to the pivot

Question 18

[Formula] Moment of a force

Answer 18

M = Fd

Question 19

[Definition] Torque of a couple

Answer 19

Torque of a couple is the product of one of the forces and the perpendicular distance between the forces

Question 20

[Definition] Equilibrium

Answer 20

A body is in equilibrium when there is no resultant force and there is no resultant torque about any point on it.

Equilibrium can also be known as dynamic equilibrium / total mechanic equilibrium

Question 21

Impt things to note:

Answer 21

1. Draw labelled force diagram to better answer the question!!!
2. Even if rotational equilibrium, if the force is slanted, need to use the vertical/horizontal component of the force. Can’t just use the slanted force straight