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力学Forces and their Effects
? Boardworks Ltd 20041 of 20 67
KS3 Physics
7K Forces and
their Effects
? Boardworks Ltd 20041 of 20 62 7
7K Forces and their Effects
Contents
Feel the force
Weight and mass
Forces in water
Friction
Summary activities
? Boardworks Ltd 20041 of 20 63 7
A force is a push, pull or twist. A force cannot be seen but
you can see how a force affects an object.
What is a force?
? Boardworks Ltd 20041 of 20 64 7
Forces activity
? Boardworks Ltd 20041 of 20 65 7
10 N 10 N
If you link two forcemeters and pull equally hard from both
ends, the forces recorded on both will be the same.
balanced forces
When forces are balanced
The forces acting on the central hooks cancel each other out
– they are equal in magnitude and opposite in direction.
Because the forces are balanced the hooks do not move.
? Boardworks Ltd 20041 of 20 66 7
11 N 10 N
What happens if the pull on one end is greater than the pull
on the other end?
unbalanced forces
movement
When forces are unbalanced
The forces acting on the hooks are no longer balanced.
Both hooks will start to move to the left – their speed will
change. This is called acceleration.
Unbalanced forces lead to a change in speed or direction.
? Boardworks Ltd 20041 of 20 67 7
Balanced or unbalanced forces?
? Boardworks Ltd 20041 of 20 68 7
7K Forces and their Effects
Contents
Feel the force
Weight and mass
Forces in water
Friction
Summary activities
? Boardworks Ltd 20041 of 20 69 7
If you rub your hands
together they get warm.
There is resistance to the
rubbing motion.
What is the name of this
resistive force called?
What causes this force?
Your hands might look smooth, but on a microscopic level
they have rough surfaces. So when you rub your hands
together you feel the resistive force of friction.
What is friction?
It is called friction.
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Friction always tries to slow moving objects down.
We say it opposes motion.
There is a maximum value for the frictional force
which depends on:
More ab
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