4.1.11

# Acceleration Due to Gravity

Test yourself

## Free Fall

If an object is in free fall, then the object’s weight is the only force acting on it. The weight of an object is the force that acts downwards on an object due to gravity.

### Acceleration due to gravity

• An object in free fall will accelerate at a constant rate. This constant rate is called the acceleration due to gravity (g).
• The average value for acceleration on Earth due to gravity is 9.81 m/s2.

## Determination of g by Freefall

By dropping an object and recording the time taken to fall a certain height, the value of g can be determined.

### Steel ball and trap door

• Set up your equipment as shown.

### Measurements

• Record the height the steel ball is at.
• Release the trap door and time how long it takes to travel the distance 'h'.
• You can use a pressure sensitive plate attached to an electronic timer.
• Repeat three times more and record the average.

### Vary h

• Measure the time taken to fall from a range of different heights.
• You should take at least 7 measurements.
• They should each be separated by a few centimetres.

### Plot graph

• Plot a graph of t² on the x axis against h on the y axis.
• The graph should be a straight line.

### Gradient

• The gradient of the graph is equal to half g.
• gradient $= \frac{1}2 g$
• So g = 2 × gradient.

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