# Physics

• Created by: shejamea1
• Created on: 12-05-15 16:13

## Speed, distance & Time

The equation for speed is:

Speed (m/s) = distance (m) divided by time (s).

The units of speed depend upon the units used in the equation.

Average speed is the total distance travelled divided by the total time taken.

Instantaneous speed only considers the distance travelled over a short period of time (in that instant).

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## Distance-time Graphs

This is a distance-time graph.

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## Acceleration

Acceleration is the rate with which an object's speed changes.

Acceleration (m/s ) = change in speed (m/s) divided by time (s).

e.g

If a car's speed increases from 10 to 30 m/s in 5 seconds.

To work out the acceleration we go:

30-10=20

20 divided by 5 =4

4m/s

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## Terminal Velocity

Terminal velocity is reached when a falling object is at it's maximum speed.

Initially a falling object accelerates due to it's weight. as it speeds up, the frictional force (air resistance) opposing the motion gets bigger untill the acceleration deduces to zero.

If frictional forces (air resistance) is larger than the object's weight, it will slow down.

Increasing the surface area, or fluid density, will increase the frictional force and therefore decrease the terminal velocity.

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## Distance-time graphs 2

The distance any object travels can be plotted on a graph against the time taken.

The gradient of the line tells us the objects speed:

A steeper line means a greater speed.

The change the distance and time can be read from the graph so the speed cvan be calculated.

For example on the graph above the red car travels 8m in 4s. Therefore 8 divided by 4 = 2.

So the car was going at a speed of 2m/s.

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