Forces and Motion

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1.2 plot and interpret distance-time graphs

A distance time graph is a graph showing the relationship between distance travelled and time taken.

Drawing a distance time graph

The Y axis should be the distance travelled from the start, meaning the bottom is time.

To plot simply mark the distance travelled at every chosen point of time: e.g every second.

Interpreting distance time graphs

A horizontal line is a stationary object: because time is still going forward but the object is not moving up or down the distance axis.

A line upwards is a object moving away from the start; a downward line is a object moving towards the start.

The steeper the line the faster the object: its doing more distance for time- more up for across.

To get a speed see how much up it goes for across. (the graph on the link below goes two up for one across that's two meters per second (2m/s))

1.3 know and use the relationship between average speed, distance moved and time

Average speed= Distance moved / time taken

1.4 describe experiments to investigate the motion of everyday objects such as toy cars or tennis balls

You could plot the time it takes for a toy car to travel and then plot a distance time graph. Then repeat at different speeds and compare the different graphs.

Alternatively, you could use a ticker tape; this makes a mark every second on the tape. If you attach the car to the end of the tape, its speed will be recorded: distance/dots = speed. For example, if you has 50 dots on a meter tape then it traveled at an average speed of (1/50) 0.02 meters per second.

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1.5 know and use the relationship between acceleration, velocity and time

Acceleration= change in velocity / time taken

a= (v-u)/t

1.6 plot and interpret velocity-time graphs

Plotting

On the Y axis of a distance time graph is velocity- speed travelled in a give direction. On the X axis is time taken from start. Note that negative velocities mean something is travelling in the opposite direction to that of the positive velocity.

Interpreting

A line going diagonally upwards shows an acceleration, if it is straight it is a constant acceleration. This is because acceleration is change in velocity over time.

A line going diagonally down wards shows a deceleration. A straight downwards line shows constant deceleration. Again deceleration is change velocity over time but the velocity is decreasing.

The steeper the line the more rapid the acceleration because the velocity us changing over less time.

A straight line is a constant velocity: you are travelling at one speed in one direction.

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1.7 determine acceleration from the gradient of a velocity-time graph

Acceleration is measured in meters per second per second: m/s/s or m/s².

This means we need to find out how many m/s are travelled every s.

Which is the same as change in velocity over time.

We can work this out by looking at a time period in the graph and seeing how much the velocity changes. For example on this graph between second 3 and second 4 the velocity changes from 0 to 4: meaning that it changes 4 m/s every 1s

4/1= 4m/s²

So effectively you do up divided by across to give acceleration.

(bbc)

1.8 determine the distance travelled from the area between a velocity-time graph and the time axis

Distance can be calculated by finding the area between the velocity time graph (line) and the time axis. If you look there is a shape formed between the two lines, find the area of this using the measure given on the sides

e.gThe width of the triangle is 4 seconds and the height is 8 metres per second. to find the area of a triangle is 1/2 x base x height so 1/2 x 8 x 4= 16

The width of the rectangle is 6 seconds and the height is 8 metres per second. So the area is 8 × 6 = 48 m. Making the overall area 16 + 48 = 64 m.

(BBC bitesize)

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1.9 describe the effects of forces between bodies such as changes in speed, shape or direction

Changes in speed

When an object is stationary it has an equal force pushing down and up. The downward force being gravity and the upward force being the surface the object is on. The object is not floating but it is not going into the ground.

When an object is accelerating it has the upwards and downwards forces but it also has forwards and backwards forces (drag and friction). The forward force is larger than the backward force when an object is accelerating.

When an object is going at a constant speed it has downward and upward forces as well as forward and backward forces. The forward and backward forces are equal, so the speed doesn't change even though the object is moving.

When an object is decelerating it has the equal upward and downward forces as well as forward and backward forces, but the backward force is larger than the forward one, slowing the object down.

Changes in shape

changes in shape affect momentum. Force= change in momentum/ time taken. An example of this is crumple zones in car decrease the force on the passengers.

Changes in direction

Which ever direction the force is greatest in will be the direction the object travels in.

1.10 identify different types of force such as gravitational or electrostatic

Different forces include:

Gravity; acting downwards

Up thrust; acting upwards

Drag; acting against the movement

Learn the direction that forces act in and you will be able to forfill this criteria

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1.11 distinguish between vector and scalar quantities

Vector

Has magnitude and a direction. For example velocity is a speed in a given direction.

Scalar

Has a magnitude. For example speed.

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