Transcript Slide 1

What stops us from falling off the surface of
the Earth?
Why is high jump so difficult?
Why do we get hit with bird poo?
Of coarse the answer is GRAVITY...
This is a non-contact force that pulls and
attracts objects towards Earth.
Without gravity, even the Earth’s atmosphere
would float off into space.
-The force of gravity is not the same on all
objects – the greater the mass of an object,
the greater the force of gravity on it.
- Mass is different to weight.
- The weight of something or someone is
usually equal to the force of gravity pulling it
down.
- The standard unit of force in the newton
(N).
- At the Earth’s surface, the force of gravity is
about 10 newtons for every kg of mass.
- Because the force of gravity is less on Mars,
a person weighs less than half their weight
on there.
Countless people fell to
their deaths during the
construction of the
Brooklyn Bridge
Gravity has impacted on the
Leaning Tower of Pisa, to turn
it from a boring old monument,
to a world renowned tourist
attraction
Gravity was the greatest
challenge for the Egyptians as
they manually hauled stone to
piece together the Pyramids
Because of gravity, the Statue of
Liberty had to shipped over
from France piece by piece and
put together in New York
Harbor
-Lets drop a piece of paper... What forces
are acting on it???
- Gravity is not the only force that acts on
falling objects.
- The way objects fall depends on the total
force acting on them, not just the pull of
gravity.
- Air in the atmosphere pushes against all
falling objects – this is called AIR
RESISTENCE and is an example of fluid
friction.
Answer the following questions:
Drop a coin from waist height
1. How many forces are acting on the coin as falls
through the air?
Drop a coin and a paper disc at the same time
1. Which object landed first?
2. What two forces were acting on the paper disc?
3. What is different about the forces acting on the
coin?
Drop the coin with the paper on top
1. Which lands first?
2. Why?
-The air resistance on a moving object increases as
the object moves faster.
- What happens to wind when you run or cycle
faster?
- When you go fast, you feel the air pushing against
your face, but when you slow down it stops.
- When an object starts to fall, it moves slowly. There
is not much air resistance. As the object speeds up,
the air resistance gets much larger.
- If an object travels fast enough, the air resistance
can become as big as the force of gravity on the
falling object. Once this happens, the objects stops
speeding up and has reached terminal velocity.