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Flashcards in Forces Deck (46)
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31

What is velocity?

It is the speed in a GIVEN DIRECTION. It is a vector quality.

32

How do you calculate the speed of an object?

Speed (m/s) = distance (m) / time (s)

33

What is acceleration? Equation?

It is the rate of change of the velocity. It is the change in velocity in an amount of time.

Acceleration (m/s2) = v-u (m/s) / time (s)

34

What does a distance time graph show us?

-gradient=speed
-flat sections=object stationary
-straight sections=steady constant speed
-levelling off=slowing down
If object is accelerating, find the gradient of tangent to the curve at that point it's speed has changed

35

What does a velocity time graph show us?

How an objects velocity changes on a journey.
-gradient=acceleration
-flat sections=steady speed
-steeper the graph=greater acceleration/deceleration
-area under sections of graph equal to distance traveled in that time

36

What is drag? How can it be avoided?

Resistance you get in a fluid (gas or liquid) air resistance is a type of drag. Drag increases as the speed increases.

Can be reduced by keeping shape of object streamlined eg train

37

What does it mean if an object is in equilibrium?

It's weight is equal to the normal contact force.

38

What is the stopping distance?

The sum of the thinking distance and the breaking distance. It is the distance it takes to stop a car.

Stopping distance = thinking distance + breaking
distance

39

What is the thinking distance? What affects this?

How far the car travels during the drivers reaction time. It is affected by:
-speed
-your reaction time- tiredness, drugs, alcohol, distractions

40

What is your reaction time? What affects it?

The distance taken to stop once the brakes are applied. It is affected by:
-speed
-road surfaces/weather
-condition of tyres
-condition of brakes

41

What happens when the brakes of a car are applied? Hazards?

-brake pads pushed onto wheels which cause friction which causes work to be done
-the work done between wheels and brakes transfers energy from kinetic energy stores to thermal energy stores

A larger braking force means a larger which can be dangerous as brakes could overheat or car could skid

42

What is another equation for momentum? (Kg m/s)

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

43

What does the conservation of momentum state?

In a closed system, the momentum before an event is the same after the event.
Eg if momentum before was 0, it would be 0 after

44

What is 'uniform acceleration' ?

When the acceleration is constant.

45

What is inertia?

The resistance an object has to a change in its state of motion

46

What are some safety features of a car?

-airbags reduce forces on head
-crumple zones absorbs crash energy and reduces force
-headrests
-braking systems
-seat belts increase time taken for body's momentum to reach zero