P2 - Physics Notes (CGP GCSE Physics Book)

As Fast As You Can:

Speed and Velocity:

- Speed is how fast something is travelling (mph, m/s etc).

- Velocity is how fast something is travelling in a certain direction (50 mph South etc).

- They're both calculated in the same way.

- Average Velocity = Displacement / Time

- Speed cameras can be used to catch speeding motorists.

1) 2 lines are painted on the road.

2) A photo is taken when a car crosses the first line, and another on the second.

3) The photos are then used to determine the cars speed.

Acceleration and Velocity-Time Graphs:

- Acceleration is how quickly the velocity of something is changing.

- It can be a change in speed or a change in direction.

- Acceleration = Change in Velocity/ Time Taken.

- It is measured in m/s².

- Velocity-Time Graphs:

1) Gradient = Acceleration.

2) Flat sections show steady speed.

3) The steeper the line, the greater the acceleration/deceleration.

4) Uphill lines are acceleration.

5) Downhill lines are deceleration.

6) The area under any section of the graph is equal to distance travelled in that time.

7) A curve means changing acceleration.

- Calculating Acceleration, Velocity and Distance from a Graph:

1) Eg. Acceleration = Gradient = Vertical Change / Horizontal Change = 30 / 20 = 1.5m/s².

2) The velocity is found by reading it off the velocity axis.

3) Distance travelled is equal to the area under the graph.

Forces:

- A force is a push or a pull. Six main forces:

1) Gravity or weight - acts straight downwards.

2) Reaction force from a surface - straight upwards.

3) Thrust / Push / Pull - speeding up

4) Drag / Air Resistance / Friction - slowing down

5) Lift - aeroplane wing etc.

6) Tension - in a rope, cable etc.

- Objects only accelerate in a particular direction if there's an overall force in that direction.

- If the forces on an object are balanced, it won't move.

Friction Forces and Terminal Velocity:

- Friction is always there and effects everything.

- If there is no force pushing something, it will stop.

- Friction acts in the opposite direction to the way an object is moving.

- It occurs between two surfaces.

- In fluids (including the air) it's called drag.

- Drag increases as the speed of…