Year 9 Physics Block 1 - free body diagrams

Year 9 Physics Block 1 - free body diagrams

By Laura Rogers

how can we represent the forces acting on it?​

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​Here's the Mars lander

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Rules for free body diagrams

​​Arrows should touch the object

Arrows don't touch object.

​​Incorrect!

​The arrows touch the object.

​​Correct :)

Multiple Choice

Is this diagram correct?

• Yes, the arrows should touch the object

• No, the arrows should not touch the object

• No, the arrows should be the same colour

• No, the arrows are different sizes

Multiple Choice

Is this diagram correct?

• Yes, all the forces are shown in Newtons

• Yes, all the forces are labelled

• Yes, all the arrows are the same size

• No, the arrows are not touching the object

The force acting all over the object is simplified, and shown as a single arrow.

​​One arrow per force

Lots of arrows.

​​Incorrect!

One arrow per force.

​​Correct :)

Multiple Select

What is wrong with these diagrams (two answers)?

• The forces are all acting in different directions

• The arrows are not touching the objects

• There is more than one arrow for each force

• The plane can't be moving if the forces are balanced

Multiple Choice

Which force is incorrectly shown?

• upthrust

• pull of gravity

• push down on the balloon

• none of them

• all of them

​And you must give the correct name of the force, e.g. weight, not gravity.

Arrows must be labelled

No labels on these arrows.

Incorrect!​

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Forces are correctly labelled.

​​Correct :)

Multiple Select

The statement at the top of this graphic is incorrect. There are also two mistakes in the diagram,. what are they?

• Normal force should act upwards

• Should say 'weight' not 'gravity'

• Arrows are not touching the object

• Arrows should be different lengths

Multiple Choice

Is this diagram correct?

• Yes, forces are correctly labelled and arrows touch object

• Yes, because all the arrows are the same length

• No, you can't use a dot for the object

• No, the normal force should be acting upwards

The longer the arrow, the larger the force.

​​Length of arrow shows size of force

In this diagram, the arrows are the same length but the magnitude (size) of the forces is different.

​​Incorrect!

​The drag is greater than the weight. There is a resultant force upwards, so the object is decelerating.

​​Correct :)

Multiple Select

This one again. Spot two mistakes this time.

• The arrows are different colours

• The arrows are not touching the object

• The arrows point towards the object

• Given the size of the forces, the arrows should be different sizes

Draw

Now answer this question and get full marks.

​How did you do?

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