Physics Module 3

Front 1

The formula for speed is: AVERAGE SPEED= DISTANCE/TIME We write 'average speed' because the speed of a car changes during a journey. Increasing the speed means increasing the distance travelled in the same time. Increasing the speed reduces the time needed to cover the same distance. The formula for average speed can be re-arranged to work out: DISTANCE= SPEED X TIME and TIME= DISTANCE/SPEED

Back 1

Distance-time graphs allow a collection of data to be shown. It is easier to interpret data when they are plotted on a graph than when they are listed in a results table. The GRADIENT of a distance-time graph tells you about the speed of the object. A higher speed means a steeper gradient. If the gradient is a straight line, the speed is constant. If the gradient is curved, then the speed changes.

Front 2

If the speed is increasing, the object is ACCELERATING. If the speed is decreasing, the object is DECELERATING. The AREA under a speed-time graph is equal to the distance travelled. The gradient of a speed-time graph is the acceleration. DISTANCE= AREA UNDER SPEED-TIME GRAPH (Phythagoras) If the speed is not chaning uniformly, the acceleration is not constant. The area under the graph is estimated to work out the distance.

Back 2

During a car journey, the speed of the car increases and decreases; it doesn't stay constant. For working out acceleration: ACCELERATION= CHANGE IN SPEED/TIME TAKEN A negative acceleration shows the car is slowing down, or decelerating.

Front 3

A vehicle may go around a roundabout at a constant speed but it is accelerating! This is because it's direction of travel is changing; it's not going in a straight line. The driver needs to appy a force TOWARDS THE CENTRE of the roundabout to change direction. This gives the vehicle an acceleration directed towards the centre of the roundabout. Any object moving along along a circular path moves TANGENTIALLY to the circle, or arc of a circle. VELOCITY is the speed of a moving object in a known direction.

Back 3

If the forces acting on an object are balanced, it's at rest or has a constant speed. If the forces acting on an object are unblanced, it speeds up or slows down. The unit of force is NEWTON (N). F=ma F= unbalanced force in N, m is mass in kg and a= acceleration in m/s^2. The equation is used to find mass or acceleration if the resultant force is known. Forces occur in pairs. They: - are the same size - are in opposite directions - act on different objects

Front 4

Thinking time, and therefore thinking distance, may increase if a driver is: - tired -under the influence of alcohol or drugs - distracted or lacks concentration. Braking distance may increase if: - the road is icy or wet - the car has poor brakes or bald tyres - the car is travelling fast. STOPPING DISTANCE= THINKING DISTANCE + BRAKING DISTANCE For safe driving, it's important to: - keep an appropriate distance from the car in front - have different speed limits for different types of road - slow down when road conditions are poor. Factors affecting braking distance: - Bigger mass - Greater speed - Worn tyres with little tread - Worn brake pads

Back 4

Work is done when a force moves in the direction in which the force acts. WORK DONE= FORCE X DISTANCE MOVED (In the direction of the force) When car brakes are applied, the brake pads are pushed against a disc. This creates a large amount of friction force that slows the car down. A car loses all its kinetic energy when it stops. The kinetic energy is transferred mainly into heat by the brakes. Kinetic energy lost= work done by brakes. BRAKING DISTANCE= WORK DONE BY BRAKES/BRAKING FORCE

Front 5

The formula for power is: POWER= WORK DONE/ TIME TAKEN A person's power is greater when they run than when they walk. The equation can be re-arranged to make: WORK DONE= POWER X TIME and TIME TAKEN= WORK DONE/ POWER

Back 5

Fuel is expensive and a car with high fuel consumption is expensive to run. Fuel pollutes the environment. - Car exhaust gases, especially carbon dioxide, are harmful. - Carbon doixide is a major source of greenhouse gases, which contribute to climate change.

Front 6

Fuel comsumption data are based on ideal road conditions for a car driven at a steady speed in urban and non-urban conditions. Factors that affect the fuel consumption of a car are: - the amount of energy required to increase its kinetic energy - the amount of energy required for it to do work against friction - it's speed - how its driven, such as excessive acceleration and deceleration, constant braking and speed changes - road conditions, such as a rough surface.

Back 6

Kinetic energy increases with: - increasing mass - increasing speed. The braking distance of a car increases with increasing speed, but not proportionally. The formula for kinetic energy is: KINETIC ENERGY= 0.5MV^2 where m is mass in kg and v is speed in m/s. When a car stops, it kinetic energy changes into heat in the brakes tyres and road. BRAKING FORCE X BRAKING DISTANCE= LOSS IN KINETIC ENERGY When the speed of the car doubles, the kinetic energy and the braking distance QUADRUPLES.

Front 7

Exhaust fumes from petrol-fuelled and diesel-fuelled cars cause serious pollution in towns and cities. Battery driven cars do not pollute the local environment, but their batteries do need to be recharged. Recharging uses electricity from a power station. Power stations pollute the local atmosphere and cause acid rain.

Back 7

Car safety

Front 8

To minimise injury, forces acting on the people in the car during an accident must be minimised. Force= mass x acceleration. Force can be reduced by reducing the acceleration by: - increasing stopping or collision time - increasing stopping or collision distance. safety features that do this include: - crumple zones - seat belt - air bags - crash barriers - escape lanes

Back 8

Falling objects

Front 9

Terminal speed

Back 9

Energy transfers

Front 10

Calculating gravitational potential energy

Back 10

How a roller coaster works