What is meant by the term ‘collision theory’?

WEEK 3

DISPLACEMENT-TIME GRAPHS

Displacement is how far an object is from its original position, so a displacement-time graph shows how this changes as time passes during a journey (or whilst the object is stopped).

Using the graph we can work out the speed of an object by looking at the steepness of the line and finding the gradient (how far up divided by how far along that section goes).

There is a more suitable physics word for ‘getting faster’. What is it?

VELOCITY-TIME GRAPHS

Velocity is speed in a fixed direction. Velocity-time graphs show how the velocity of an object varies during the time of a journey.

Velocity can be a negative value if an object is travelling in the opposite direction to the one chosen, for example if you choose ‘upwards’ as the positive direction then ‘downwards velocities’ would be negative.

Like with displacement graphs, the gradient of the line can tell us something – in this case the acceleration.

Acceleration = change in velocity/time

HIGHER ONLY

On higher exams you might be asked to determine the distance an object has travelled on the journey, which is the area under the graph up to that point.

The area can be split into rectangles and triangles, and the usual maths rules used to calculate them.

You might also, as with displacement graphs, be asked to find an acceleration at a certain point on a curve using the gradient of a tangent.

FORCES AND MOTION

NEWTON’S LAWS OF MOTION

NEWTON’S 1ST LAW

Newton’s 1st Law means UNBALANCED FORCES cause ACCELERATION (note - this is not a statement of Newton’s 1st Law, this is just how it works.) If the object is originally AT REST (stopped) it will SPEED UP FORWARDS or BACKWARDS. If the object is already moving with a CONSTANT VELOCITY it will SPEED UP in the direction it’s moving or SLOW DOWN. (It might even start to go backwards if the force acts for long enough!) 1. State Newton’s 1st law of Motion.

NEWTON’S 2ND LAW

Newton’s 2nd Law is the equation F = m x a, which tells us how much force is needed to make a mass accelerate at a certain rate.

F = m x a a = F/m m = F/a

1N of force on 1kg of mass causes 1m/s² of acceleration. 2. Calculate the acceleration on this block if all the forces are shown.

NEWTON’S 3RD LAW

Newton’s 3rd Law is that every force or action has an equal, opposite reaction force. What this means is that when one object causes a force on another object, an equal force acts back on the first object.