# Movement + Forces

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Distance-Time Graphs - a distance time graph is a graph which plots the distance (y axis) compared to time (x axis).

A diagonal line repersents someone traveling at a constant speed.

Horizontal lines indicates that the object has stopped moving.

This type of grpah can also be used to calcualte the speed of the object by using this equation:

Speed (m/s) = Distance (m) / Time (s)

Speed-Time Graphs - these graphs plot the speed (y axis) against time (x axis).

An upwards diagonal line indicates accelaetation. (The steeper the line the faster the acceleration)

A horitzonal line repersents an object moving at a contant speed.

A diagonal downwards line shows decceleration.

We can use the equation for speed and the graph to calcualte acceleration:

Acceleration (m/s/s) = Change in velocity (m/s) / Time (s) (Velocity is another word for speed. If the speed in increasing it's a postice velocity. If the speed is decreasing it's negative velocity.)

Forces - are basically pushes and pulls. If they act on an obejct it can cause it to change speed or direction.

A good way to imagine forces is thinking about two teams playing tug of war. If each team pull on the rope with an equal force the rope won't move. It will remain stationary. (Resultant force = 0N) However if one team applies more force than the other the rope will move in the direction of the larger force (the stronger team). The difference between the two forces is called a resultant force which travels in the same direction of the object.

For example if the Left team of tug of war had a force of 500N and the Right team had a force of 250N the rope would move towards the direction of team L and the resultant force would be 250N  (500N - 250N) towards team L also.

When objects start to move they quickly build up forces in the oppisite direction of movement. These are usually air resistance (drag) and friction.

There are three things you need to know: