Full throttle physics

how to find the average speed

the average speed = total distance/total time

e.g if the time is measured in hours and the distance is measured in cm then its cm/h

how to find the average time

time = distance/speed

how to find the average distance

distance = speed x time

what is acceleration

acceleration is change in velocity/time or v-u/t

acceleration is any change in velocity

positive acceleration means speeding up

negative acceleration means slowing down

usually the unit for acceleration is m/s2

what is Isaac newtons second law and what is the equation that goes with it

newtons second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass

the equation is F=ma

Distance

The TOTAL amount of ground an object covers while moving. Distance does NOT care about direction at all — it only cares about how far something travelled altogether. If you walk around in circles for 2 km and end up where you started

Displacement

The SHORTEST straight-line distance between an object’s starting point and ending point

Difference between distance and displacement

Distance measures the ENTIRE path travelled

Speed

How FAST an object is moving. Speed tells you how much distance is travelled in a certain amount of time

Velocity

The speed of an object IN A SPECIFIC DIRECTION. Velocity is basically speed with direction added onto it. Saying “20 m/s” is speed

Difference between speed and velocity

Speed only tells you how fast something moves

Displacement-time graph

A graph that shows how an object’s displacement changes over time. It helps show whether an object is moving

Gradient of a displacement-time graph

The gradient (slope) of a displacement-time graph tells you the VELOCITY of the object. A steeper gradient means a faster velocity.

Horizontal line on a displacement-time graph

A horizontal line means the object is NOT MOVING because its displacement is not changing over time.

Steep gradient on a displacement-time graph

A steeper gradient means the object is moving faster because the displacement is changing more quickly.

Velocity-time graph

A graph showing how an object’s velocity changes over time. It can show acceleration

Gradient of a velocity-time graph

The gradient (slope) of a velocity-time graph represents the ACCELERATION of the object.

Positive gradient on a velocity-time graph

Means the object is accelerating or speeding up.

Negative gradient on a velocity-time graph

Means the object is decelerating or slowing down.

Horizontal line on a velocity-time graph

Means the object has constant velocity because the velocity is not changing.

Acceleration

The rate at which velocity changes over time. Acceleration can mean speeding up

Acceleration formula

a = (v − u) / t

a in the acceleration formula

Acceleration

v in the acceleration formula

Final velocity

u in the acceleration formula

Initial velocity

t in the acceleration formula

Time taken

What acceleration actually means

Acceleration tells you how quickly an object’s velocity changes. The faster the change happens

Positive acceleration

Occurs when an object speeds up over time.

Negative acceleration (deceleration)

Occurs when an object slows down over time.

Zero acceleration

Means the object’s velocity is not changing. The object could be stopped OR moving at a constant velocity.

Newton’s First Law of Motion

An object will stay at rest or continue moving at constant velocity unless acted upon by an UNBALANCED force.

Inertia

The tendency of an object to resist changes in its motion. Objects REALLY want to keep doing whatever they’re already doing 😭

Example of Newton’s First Law

When a car suddenly stops

Unbalanced forces

Forces that are NOT equal and opposite. Unbalanced forces cause changes in motion

Balanced forces

Forces that are equal and opposite

Effect of unbalanced forces

Unbalanced forces can make an object speed up

Newton’s Second Law of Motion

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

Newton’s Second Law equation

F = ma

F in F = ma

Net force

m in F = ma

Mass

a in F = ma

Acceleration

What Newton’s Second Law means

A bigger force causes a bigger acceleration

Example of Newton’s Second Law

An empty shopping trolley accelerates much easier than a fully loaded one because it has less mass.

Newton’s Third Law of Motion

For every action force

Action-reaction pairs

Two forces that are equal in size

Why action and reaction forces do not cancel out

They act on different objects

Example of Newton’s Third Law

A swimmer pushes water backwards

Momentum

The quantity of motion an object has. Momentum depends on BOTH mass and velocity.

Momentum formula

p = mv

p in the momentum formula

Momentum

m in the momentum formula

Mass

v in the momentum formula

Velocity

What momentum means

Objects with more mass or more velocity have more momentum and are harder to stop.

Law of Conservation of Momentum

The total momentum before a collision equals the total momentum after the collision

Example of conservation of momentum

When two billiard balls collide

How seatbelts reduce force in crashes

Seatbelts increase the time taken for passengers to stop moving during a crash

How airbags reduce force in crashes

Airbags increase stopping time and spread the force over a larger area

How crumple zones reduce force in crashes

Crumple zones absorb energy and increase collision time

Displacement-time graphs

A graph showing how displacement changes over time. The gradient (slope) tells you the VELOCITY of the object. A steeper slope means faster velocity

Convert between units of speed

To convert speed units you need to change BOTH the distance unit and the time unit correctly. For example

What is displacement

Displacement is the SHORTEST straight-line distance between the starting point and ending point of an object

Calculate force

Force is calculated using Newton’s Second Law. Multiply mass by acceleration using the formula F = ma. The answer is measured in newtons (N).

Use an equation to find an unknown

Substitute the values you already know into the formula

Calculate acceleration

Acceleration is found by dividing the change in velocity by time using the formula a = (v − u) / t. Acceleration measures how quickly velocity changes over time.

Speedometer average speed and instantaneous speed

A speedometer shows INSTANTANEOUS speed

How to find average speed

Find the total distance travelled

How to find instantaneous speed

Instantaneous speed is the speed at a specific moment in time. On a graph

How to find distance travelled

Distance travelled can be found using the formula Distance = Speed × Time.

Reaction time

Reaction time is the time it takes for a person to respond to a situation or stimulus

Breaking distance

Braking distance is the distance a vehicle travels AFTER the brakes are applied until the vehicle fully stops.

Stopping distance

Stopping distance is the TOTAL distance travelled from the moment a driver notices a hazard to the moment the vehicle completely stops. It equals reaction distance plus braking distance.

How to find stopping distance

Add the reaction distance and braking distance together to get the total stopping distance.

What is weight force

Weight force is the force caused by gravity pulling on an object. Weight depends on both mass and gravitational field strength.

How to calculate weight force

Weight force is calculated using the formula W = mg

What is net force

Net force is the OVERALL force acting on an object after all forces are combined. Net force determines whether an object accelerates

How to calculate net force

Add forces acting in the same direction and subtract forces acting in opposite directions. The remaining force is the net force.

Draw forces acting on a body in a situation

Use a force diagram with arrows showing all forces acting on the object. The arrows should point in the direction of the force and be labelled clearly

Analysing graphs

Look carefully at the shape and gradient of the graph. On displacement-time graphs the slope shows velocity