# P3 Forces (Moments, CoM, Stability)

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What is a lever?
Machine that helps us do work more easily (small->large force)
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What is a pivot?
A point at which something turns.
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What is the centre of mass/gravity?
The point where all weight/mass appears to act.
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Step one of finding the CoM/G in an irregular shaped lamina.
1)Freely hang the lamina from a retort stand.
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Step two.
Hang plumb line from the same point as the retort stand.
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Step three.
Mark plumb line on lamina with x's and join together.
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Step four.
Rotate and repeat process with plumb line. Different hole
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Step five.
Where the two lines cross will be the centre of gravity/mass.
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Step six.
To check, rotate and do with a third point.
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How do we determine whether an object will topple or not?
The position of an object's centre of mass/gravity will.
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How do we increase the stability of an object?
1)Lower the COG. 2)Increase the area of the base.
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Give any two examples of this being used.
eg/ wine glass, traffic cone -a larger base/mass at the bottom
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How do we determine toppling from tilting?
Line in base=NOT TOPPLE Line outside base=WILL TOPPLE
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What is a moment?
Any turning effect which is caused by a force. (a spanner)
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What are the two parts of a lever?
Pivot and the rod (the body of the lever)
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What is the formula for a moment?
Moment,M (Nm)=Force,F (N) x distance,d (m)
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On a seasaw, how can a large person reduce his force applied?
Sit closer to the pivot (less distance)
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How can the seasaw be balanced if there is a large person and a small person?
Small person=large distance, large person=small distance
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How do we know if the moments are balanced on either side of the pivot?
The object will not turn.
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Give a simplified write out of the principle of moments.
Total anticlockwise moments=total clockwise moments
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What is the time period of a pendulum?
Time taken-swing from 1 side to other then back to orginal point
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What is the equation of finding the time period of a pendulum?
Time period(s)=1/frequency, F
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What are the factors of determining the time period?
Length. But not the mass of it or how high it's swung from.
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True or false. Liquids are compressible.
False. Liquids are virtually incompressible.
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Therefore, where is the pressure transmitted?
In ALL DIRECTIONS
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How do we find the pressure in a liquid?
Pressure, P(Pa)=Force, F(N)/Area, A(m2)
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What is the same for both master and slave pistons?
Pressure
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If the work done is the same for both pistons, what should happen to the distances they travel?
They should move proportional to the force given and work done
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Eg/ On the master, if there is a small force and large distance, how much should the large piston rise?
A smaller amount.
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What is velocity?
Vector quantity of speed and direction
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In circular motion, the speed is the same but the object continues to accelerate. Explain why.
It is constantly changing direction. So it's accelerating
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What is the centripetal force?
A resultant force to cause the object to accelerate. (N's 1st law)
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Where is the centripetal force always directed to?
The centre of the circle
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What provides the centripetal force on a rope/wire?
Tension
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What provides the centripetal force on a track/road?
Friction
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What provides the centripetal force for satellites in orbit?
Gravitational attraction between satellite and Earth
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How do you increase the centripetal force?
Increase: mass and speed of object. Decrease: radius of object
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## Other cards in this set

### Card 2

What is a pivot?

#### Back

A point at which something turns.

### Card 3

#### Front

What is the centre of mass/gravity?

### Card 4

#### Front

Step one of finding the CoM/G in an irregular shaped lamina.

Step two.