TOPIC 1 - Forces and Motion

State an Equation linking mass, velocity and Momentum

Momentum (kg m/s) = Mass (kg) x velocity (m/s)

P = m x V

Explain what is meant by conservation of momentum

Total momentum before a collision (or explosion) is equal to the total momentum after the collision (or explosion).

*Remember, momentum is a vector, so its direction is important.

State an equation linking force, change in momentum and time

Force = Change in momentum / time taken

F = Mv - Mu / t

Explain how safety features such as seatbelts, crumple zones, and airbags reduce the risk of injury in an accident

All these features increase the stopping time during a collision by applying a force for a longer period of time. Therefore, as stopping time increases, the force applied to the driver decreases; therefore, the risk of injury decreases.

Explain what Newton's third law states about forces

It states, 'for every action, there is an equal put opposite reaction. This means all forces come in pairs. Within these pairs, two forces have equal size but they act on different bodies in opposite directions (towards or away from each other)

What does the "centre of gravity" of an object mean?

A point where all the weight of the object acts. For uniform objects, it is at the object's centre. As the centre of gravity gets lower, the stability of the object increases

What is meant by 'moment'? When does it occur? Is it scalar or vector.

Its the turning effect of force. It occurs when a force is applied away from the pivot (turning point) of the object perpendicularly.

Its a vector quantity. Can be clockwise or anticlockwise

How do you calculate the moment of a force?

Moment = Force x Perpendicular distance from pivot

State two conditions for an object to be considered in equilibrium

Forces must be balanced (no resultant force)

Clockwise Moment = Anticlockwise Moment

Explain Hooke's Law

Refers to when the extension of a spring is directly proportional to the force exerted to it, up to the limit or proportionality.

Also known as the Spring Constant

Explain Newton's first law

An object that is in motion stays in motion until a force acts upon it.

An object that is at rest, stays at rest until a force acts upon it.

Explain Newton's second law

An object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to the object's mass

What is plastic deformation

A permanent deformation in an object once a load is removed. It now cannot return to its original shape.

Define Terminal velocity

The maximum velocity an object can reach when falling through a liquid. Occurs when resistive forces are equal to the object's weight.