Transcript The Physics of Forces

Is gravity real or does the Earth just suck?
New End Primary School
Tuesday 31st March
Aristotle: for an object to continue
moving there must be a force acting on it.
It is understandable that he thought this
was the case:
In the seventeenth century Galileo argued that
objects keep moving unless acted on by a force,
for example friction.
NEW END PRIMARY SCHOOL
TUESDAY 31ST MARCH
It’s easy for us to imagine a situation
where there is no friction.
If Aristotle had been right, this would
happen…
Newton later said:
Objects continue to move
in a state of constant
velocity unless acted upon
by an external net force.
1ST LAW.
Newton
Astronauts need to beware!
Newton
Newton also said:
“Every action has an equal
and opposite reaction.”
- His 3rd law.
Which explains why guns recoil and
how rocket engines work.
PUSH
PULL
TWIST
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TUESDAY 31ST MARCH
move
faster
move
slower
change
shape
stop acceleration
moving
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start
moving
change
direction
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NEW END PRIMARY SCHOOL
TUESDAY 31ST MARCH
FORCE
measured in
NEWTONS
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Weight of
an apple
≈ 1 Newton
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Force of Floor acting on Box
Force from floor on box
cancels gravity.
If the floor vanished, the
box would begin to fall.
Force of Earth acting on Box (weight)
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TUESDAY 31ST MARCH
Try to suck the ball
through the straw
Straw
Ping-pong ball
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The arrow represents the
force of gravity
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TUESDAY 31ST MARCH
FORCES ARE
BALANCED
To stop
gravity, we need an
upward force.
FORCES ARE
NOT
BALANCED
The ball does not fall when….
ACCELERATION
We can draw this by having
arrows of the same weight.
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TUESDAY 31ST MARCH
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TUESDAY 31ST MARCH
THRUST
FRICTION
AIR
RESISTANCE
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GRAVITY
TUESDAY 31ST MARCH
For example
What
happens
when
when
a driver
there who
aretravelling
is
unbalanced
at constant
forces acting
speed
on an object?
accelerates
or puts on the
brakes.
Accelerate:
drive
Brake:
drag
Speed decreases until Speed
drag increases until drag
matches drive again. grows to match drive.
GRAVITY
LIFT
FRICTION
AIR
RESISTANCE
MAGNETISM
UPTHRUST
THRUST
NEW END PRIMARY SCHOOL
ELECTRICITY
TUESDAY 31ST MARCH
1. When Isaac Newton discovered gravity, what knocked the sense in to him?
2. Which force keeps us on the Earth? Try sucking up the different balls with a
straw.
3. Thurst is a powerful force that moves things forward. Which machines rely on
clever design and thrust to keep them in the sky? Can you find any in the class
room?
Try throwing the machines! Who can get them furthest?
4. When two magnetic objects are bought near each other, they can attract or
repel. Can you find any magnetic objects in the room?
5. Compasses work based on magnetism- they feel the magnetic field of the
Earth. Point your compass to North!
6. When items move across rough surfaces, they lose energy and slow down due
to friction. Try and find something that would cause a car to feel friction.
7. When objects fall to the ground they slow down due to air resistance. What do
you think would have lots of air resistance?
8. When we turn a light switch, little electrons carry forces which cause material
in the light bulb to heat up and emit light. Find where you think there is
electricity in the room!
NEW END PRIMARY SCHOOL
TUESDAY 31ST MARCH