4.1 Forces, Density, and Pressure

Question 1

4.1.1 Where does the weight of an object act at?

Answer 1

It acts from the centre of the object.

Question 2

4.1.2 Define the moment of a force

Answer 2

A moment is the turning effect of a force.
But also…
A moment is the product of the force and the perpendicular distance from the pivot.

Question 3

4.1.2 What is the relationship between moment, force, and perpendicular distance from the pivot?

Answer 3

Moment = Force * Perpendicular distance from the pivot
Moment in Nm
Force in N
Distance in m

Question 4

4.1.3 What is a couple?

Answer 4

A couple is a pair of forces to produce rotation only.

Question 5

4.1.3 What are the conditions required for a couple?

Answer 5

• Equal in magnitude.
• Opposite in direction
• Perpendicular to the distance between them
• Produce a resultant force of 0 so due to Newton’s second law, it does not accelerate.
• Size of turning effect is called torque.

Question 6

4.1.4 What is torque?

Answer 6

Torque is the rotational force that causes an object to turn or twist.