AQA GCSE PHYSICS

What is speed?

how fast something is going

How do you work out the speed?

speed= distance ÷ time

What is velocity

speed with direction

What do distance-time graphs show?

how something is travelling over a period of time

What is the gradient of a distance-time graph equal to?

speed- how fast the object is travelling

What does the downwards gradient on a distance-time graph show?

it means its going back towards its starting location

What do the flat sections on a distance-time graph mean?

it's stationary

What do straight up hill or down hill sections mean?

it's travelling at a steady speed

The steeper the distance-time graph...

the faster it's going

What do curves represent in a distance time graph?

acceleration (steepening curve) or deceleration (leveling off curve)

How to work out the speed on a distance-time graph?

the change in y ÷ the change in x

What is acceleration?

how quickly the velocity is changing

What can the change in velocity be?

change is speed or a change in direction

What is the formula for acceleration?

acceleration= change in velocity ÷ time taken

What does the gradient equal on velocity-time graph?

acceleration

What does the flat sections on a velocity-time graph represent?

steady sped

The steeper the velocity-time graph...

the greater the acceleration or deceleration

What do the uphill sections mean on a velocity-time graph (/)?

acceleration

What do the downhill sections mean on a velocity-time graph ()?

deceleration

What does the area under any section of the velocity-time graph (or all of it) mean?

distance travelled in that time interval

What does a curve mean on a velocity-time graph?

changing acceleration

What is the unit of acceleration?

m/s²

What are gravity's two important effects?

• on the surface of a planet, it makes all things accelerate towards the ground

• it gives everything a weight

What is mass?

amount of stuff in an object

What is the unit of mass?

kg

What is weight?

the pull of the gravitational force towards the centre of the Earth

What is the unit of weight?

newtons

What is the formula relating mass, weight and gravity?

weight= mass x gravitational field strength

What is the resultant force?

the overall force on a point/object

How do you calculate the resultant force?

one force + another force

If resultant force is 0 it means that...

the object won't move

If there is no resultant for on a moving object it means that...

it will move at a constant velocity

If the resultant force on an object is not 0 it means that...

the object will accelerate in the direction of the force

What does a non-zero resultant force produce?

acceleration

What is the formula for resultants force?

resultant force (N)= mass (kg) x acceleration (m/s²)

What are the different forms of acceleration?

speeding up, steady speed, starting

When two objects interact, the forces they exert on each other are...

equal and opposite to each other

Friction is always there to...

slow things down

Friction regarding direction of movement...

acts in opposite direction

How can we reduce air resistance?

bykeeping shape streamlined

Drag increases as...

the speed increases

What is the terminal velocity?

maximum speed an object reaches and will then remain at a steady speed

What factors does terminal velocity depend on?

shape and area

What factors affect your total stopping distance?

thinking distance and braking distance

What is the reaction time?

the time between the driver spotting the hazard and taking action

factors affecting thinking distance

• how fast you're going

• how dopey you are due to alcohol, fatigue, drugs or carelessness

• bad visibility due to weather, or bright oncoming lights

• distractions

What are the factors affecting your braking distance?

• how fast you're going

• how good brakes are

• how good tires are, how good grip is on road- ice/rain

What happens when a force moves an object?

energy is transferred and work is done

What is the formula or work done?

work done= force x distance

What is gravitational potential energy?

it is energy that an object has depending on its height, the work done against the force of gravity

What is the formula for gravitational potential energy?

gravitational potential energy= mass x g x height

What is kinetic energy?

anything that is moving has kinetic energy

(the more it weighs, the faster its going, the bigger the kinetic energy will be)

What is the formula for kinetic energy?

1/2 x mass x speed²

For a car to slow down kinetic energy must be...

converted into other types of energy

For a car to stop, the kinetic energy must be...

converted into heat energy as friction between the wheels and the brake pads, causing the temperature in the brakes to increase

How do you calculate kinetic energy gained when falling?

kinetic energy gained= potential energy lost

What can potential energy be transferred into?

heat and sound energy

Elastic objects are...

objects that will return to its original shape when bent or shaped

What is the energy stored in an elastic object when bent?

elastic potential energy

The extension of an elastic object is...

directly proportional to the force applied

What is the equation that links together extension, spring constant and force?

force (N)= spring constant (n/m) x extension (m)

What happens when you pull an elastic object beyond its limit of proportionality?

it will not extend as much with the same force due to the limit of proportionality

What is power?

the rate of energy transferred

What are powerful machines?

a machine that transfers a lot of force in a short space of time

What is the unit of power?

watts or joules per second

What is the formula for power?

power= work done (or energy transferred) ÷ time taken

What is the definition of momentum?

a property of moving objects- size and direction (it is a vector quantity)

What is the formula of momentum?

momentum (kg m/s)= mass (kg) x velocity (m/s)

What is conservation of momentum?

in a closed system of momentum, total momentum before an event is the same as after

In what way do forces cause changes in momentum?

• forces act on an object cause a change in momentum

• larger force means a faster change of momentum

• if someones momentum changes very quickly (e.g. in a car crash) the forces on the body will be very large, and more likely cause an injury

Why are cars designed with safety features?

• to slow people down over a long time when they have a car crash

• the longer it takes for a change in momentum, the smaller the force

What do breaks do?

reduce the kinetic energy of the car by transferring it into heat energy

What is the difference between standard brakes and regenerative brakes?

standard brakes= kinetic energy into heat energy

regenerative brakes put motor running backwards- electricity generated and stored

How are cars designed to convert kinetic energy safely in a crash?

• crumple zones at front and back of car

• seat belts

• air bags

• side impact bars

What do crumple zones do?

• crumple upon impact

• cars kinetic energy is converted into other forms of energy by the car body as it changes shape

• the increase the impact time

• decrease the force produced by the change in momentum

What do seat belts do?

• stretch slightly

• increase the time taken for the wearer to stop

• this reduces the forces acting in the chest

• some kinetic energy of the wearer is absorbed by the seat belt stretching

What do airbags do?

• slow you down more gradually

• prevent you from hitting the hard surfaces inside the car

What do side impact bars do?

• strong metal tubes fitted into car door panels