Effects of Forces.ppt

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KS3 Physics
7K Forces and
their Effects

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7K Forces and their Effects
Contents
Feel the force
Friction
Forces in water
Weight and mass
Summary activities

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A force is a push or a pull. A force cannot be seen but you
can see how a force affects an object.
What is a force?

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What type of force?

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10 N 10 N
If you link two newtonmeters 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.

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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.

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In which direction will these stationary objects move?
Balanced or unbalanced forces?

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Contents
Feel the force
Friction
Forces in water
Weight and mass
Summary activities

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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 about friction
Friction is created whenever two touching objects or
surfaces move past each other.
Friction also occurs when things move through air.
This is called air resistance or drag.
 the force pushing the two surfaces together;
 the state of the surfaces in contact.

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One more? Probably
the most important…
Label all sources of friction that can act on this bike.
tyre and road
brake pad
and rim
wheel bearing
wheel
bearing
pedal bearing
links in chain
air resistance or “drag”
What are the sources of friction?

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Effects of frictional forces

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Contents
Feel the force
Friction
Forces in water
Weight and mass
Summary activities

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upthrust
friction
thrust
weight
What is thrust? The force that pushes an object forward.
What is upthrust? The force that pushes an object upwards
in a liquid or a gas, also called buoyancy.
Forces in water

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upthrust
or buoyancy
thrust
air
resistance
friction
weight
Label the forces acting on the ferry as it sails to France.
Ferry forces

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What happens to the weight of the ship?
What happens to the upthrust on the ship?
Which is the largest force - weight or upthrust?
increases
both equal
increases
The ferry arrives at Calais and is loaded with travellers.
Changing forces

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Contents
Feel the force
Friction
Forces in water
Weight and mass
Summary activities

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Mass and weight are not the same!
What are mass and weight?
Mass is the amount of matter in an object and is
measured in kilograms. Mass is not a force.
Weight is a force and is caused by the pull of gravity
acting on a mass . Like other forces, weight is measured
in newtons and has both magnitude and direction.
Mass will have the same value anywhere in the Universe,
including space.
Weight has different values depending on where you are
in the Universe.

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Weight and mass on the Moon
The force of gravity is less on the
Moon than it is on Earth. This is
because the Moon has a smaller
mass than the Earth.
However, the astronaut still has the
same body and the same mass: he
just weighs less because gravity is
weaker on the Moon.
Any object will weigh less on the
Moon than it does on Earth.
An astronaut could jump 20 feet
into the air on the Moon because
gravity is less.

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A scientist should never say:
“She weighs 50 kilograms,”
but should always say:
Talking about weight and mass
“She has a mass of 50 kilograms”.
“Her weight is about 500 newtons”.
Alternatively, the scientist could say:
“The gravitational force acting on her mass is
about 500 newtons”.
This is the same as saying:

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Contents
Feel the force
Friction
Forces in water
Weight and mass
Summary activities

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Glossary
 air resistance – A frictional force that acts against an
object moving through air.
 force – A push or a pull, measured in newtons (N).
 friction – A force that occurs between two surfaces
rubbing against each other.
 gravity – The force of attraction between two objects.
 mass – The amount of matter that an object is made of,
measured in kilograms (kg).
 thrust – A force that pushes an object forwards.
 upthrust – A force that pushes an object upwards.
 weight – The force caused by gravity acting on an object,
measured in newtons (N).

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Anagrams

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Multiple-choice quiz

Effects of Forces.ppt

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