Turning Forces and Centre of Gravity Chapter 42
Turning Forces and Centre of Gravity
Chapter 42
What is a turning force?
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Turning Forces
A turning force is something that would allow us to apply a much greater force than pulling or
pushing an object like moving a rock
It makes use of something called a lever
A lever is a rigid body which is free to turn about a fixed point called the fulcrum
Turning Forces
The Fulcrum is the part about which the lever turns
The effort is where the force is applied
The load is where the force takes effect
Everyday examples
Moments
The turning effect of the force is called the moment of the force and it depends on 2 things:
1. The size of the force (measured in Newton's)
2. The distance (in meters) from the fulcrum to where the force is applied
Some Math…
Moment = Force x Distance from the Fulcrum
Balancing Moments
If the moments are equal on both sides of the see saw it is balanced
Some Examples
A metre stick is suspended from its centre of gravity which is at its midpoint.A force of 3 N acts on the stick at the 90 cm mark and a force of F newtons acts on the stick at the 20 cm mark. Calculate force F.
The Law of The Lever
When a lever is balanced, the clockwise and anti-clockwise moments are equal
The Experiment
You will need :
1. A meter stick2. Retort stand3. Weights4. Table to record results
* 100g = 1N
Table
Method
1. Hang the meter stick from the retort stand at the 50cm mark or until it is balanced
2. Hang a 1N weight on the RHS and a 2N weight on the LHS so they balance eachother
3. Note the distances of each weight from the fulcrum and calculate the moment
4. Repeat placing the weights in different positions or adding more weight
Just for fun
Try and find the weight of an unknown object…
How do you think we can do this?
*Phet annimation
Homework
Q3, 4 Page 286
In your pairs bring in a piece of cardboard for next week!
Centre of GravityPage 281
Challenges!
Volunteers Please
Centre of Gravity
The center of gravity of an object is the point through which all the weight of the
object appears to act
Investigation to find the centre of gravity of Irregularly Shaped Cardboard
Apparatus:
• Cardboard• Retort Stand• Cork• Pin• Weight• String• Pencil• Ruler
Equilibrium and The Stability of Objects
An object that is balanced and not moving is said to be in equilibrium. There are three states of equilibrium : stable, unstable and neutral
An object can be made more stable by:• giving it a low centre of gravity• giving it a wider base
An object will topple if a vertical line through its centre of gravity falls outside its base.
States of Equilibrium