tion of the resultant force.
In picture A, the forces are unbalanced, and the downward force is much greater than the upward force so the ball will move quickly in a downward direction. In picture B the upward force is slightly bigger than the downward force so the ball will move upwards but very slowly. In picture C, the upward force is much greater than the downward force so the ball will move up quickly, in the direction of the resultant force.
Get a light ball (or if you haven’t got one to hand just a screwed up ball of paper will do, and sit opposite someone else at a table. Put the ball between you and try the following scenarios, noting what happens to the ball’s speed and direction of movement. Put the ball back between you after each scenario.
1) You blow the ball gently, whilst your partner just sits and watches.
2) You blow the ball with as much puff as you can muster, and your partner blows the ball back at the same time, in the opposite direction, with a gentle blow.
3) Now repeat scenario b) but as the ball begins to move, your partner continue s to blow gently but you stop blowing completely.
Hopefully in scenario a) the ball moved towards your partner at quite a slow speed. The resultant force was unbalanced, so you caused the ball to start to move. But in scenario b), I imagine it moved in the same direction but with quite some speed! But in scenario c) hopefully, the ball started to move towards your partner then did an about-turn and started to come towards you. The resultant force would have changed when you stopped blowing which caused the ball to change direction.
Try to think about some everyday examples that you can apply your knowledge to, where unbalanced forces have caused you to start moving, speed up, slow down or change direction.
Step 4: Apply Your Knowledge to New Examples
Look at the image below and have a go answering the following together.
Although the direction of movement remains the same, describe what is happening to the speed of the bike in A, B and C.
Are the forces on the skydiver balanced or unbalanced?
Mark thinks that the yellow car is accelerating in this picture. Is he right? How do you know?
Step 5 - Putting it into Practice
Now, you’ve covered this together why not put this to the test and assign your child the following 5 activities in this order.
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1) A=constant /steady speed, B=Accelerating, C=Decelerating
3) Mark is wrong, The resultant force is acting backwards so the car will be slowing down, or reversing.
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