Centre of Gravity Centre of Mass CoM This is a point on an object where the total mass acts as if it is concentrated Also know as the centre of gravity where the weight force acts on an object ID: 724744
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Slide1
Centre of Mass ~
CoM
or
Centre of GravitySlide2
Centre of Mass ~
CoM
This is a point on an object where the total mass acts as if it is concentrated. Also know as the centre of gravity ~ where the weight force acts on an objectSlide3
Centre of gravitySlide4
Centre of gravity is important for balancingSlide5
Stability
I’m instable.Slide6
My head is big for my body compared to an adult’s head. That’s why I find it harder to balance. Slide7
This lamp has a very heavy base. It will right itself if it is knocked over.Slide8
Poor balance produces an overall turning force.
This requires a turning force in the opposite direction to counteract it.Slide9
Centre of gravity is well behind the heel of the leading leg. This allows progressive loading of the leading leg.
Centre of gravity much closer to heel. This means that the loads on the heel, ankle, knee and pelvis rise sharply.Slide10
Centre of gravity located outside bodySlide11Slide12Slide13Slide14
SPOT THE Centre of Gravity
What if he straightened his legs?
That
would move his centre of gravity to the right, and he would unbalance, tipping clockwise.Slide15Slide16Slide17
Why does this balance? The weight of the hammer is acting at a point directly below where the ruler overlaps the table.Slide18
it is possible for an object’s centre of gravity to be outside the object.Slide19Slide20Slide21
Do a ‘Measured press – up’ to determine your
CoM
…
How
to find Human
centre
of
gravity / Mass??Slide22
Conditions for Equilibrium
S
F = 0St = 0
the total of all the clockwise torques=
the total of all the anti- clockwise torques
F
d
Torque ~ Turning Force e.g. the force used to open a doorSlide23
x
3
=
20 cm
3 kg
2 kg
p
F
s
= ?
x
2
=
?
2nd Condition
of Equilibrium
1st Condition
of Equilibrium
A massless
meter stick
What is the
Distance x
2Slide24
assume
S
t
= 0
Calculating the position of the Center of Mass
System
~ a group of objects
A single object has a CoM, systems also have a CoMSlide25
Radius of the Earth = 6.38 x 10
6
m
Mass of the Earth (M
1
) = 5.97 x 10
24
kg
Radius of the Moon = 1.74 x 10
6
m
Mass of the Moon (m
2
) = 7.35 x 10
22
kg
Distance between the centre of the Earth and the centre of the moon = 3.84 x 10
8
m
Calculate the position of the centre of mass (
c.o.m
) between the Earth and the Moon.
Compare your answer with the Earth's radius.Slide26
Calculate the position of the centre of mass between the Earth and the Moon.
Radius of the Earth = 6.38 x 10
6
m
Mass of the Earth (M
1
) = 5.97 x 10
24
kg
Radius of the Moon = 1.74 x 10
6
m
Mass of the Moon (m
2
) = 7.35 x 10
22
kg
Distance between the centre of the Earth and
the centre of the moon = 3.84 x 10
8
m
correct
sig. fig (3).
correct answer
Taking the centre of the Earth as the reference point, i.e., x
1
= 0
Moon
Earth
d
2. Comparing
this distance with the radius of the Earth. The
c.o.m
is roughly 2/3 from the centre of the
Earth i.e. inside
the Earth.