AQA Physics Unit 3

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  • Created on: 21-04-11 16:43
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What is a moment?
The turning effect of a force is called a moment.
How do you increase a moment?
You can increase it by increasing the size of the force or using a greater distance.
If the moment is 35Nm when the perpendicular distance was 10m what is the size of the force applied?
35Nm = force x 10m
Force = 35Nm/10m
Force = 3.5N
What is the centre of mass of an object?
This is the point at which all of its mass may thought to be concentrated.
What happens in a suspended equilibrium?
When a suspended object is in equilibrium then it's centre of mass is directly beneath its point of suspension.
Where is the centre of mass of objects?
For a symmetrical object, the centre of mass will be along its line of symmetry.
How do you find the centre of mass of a flat card?
You suspend it freely from a pin and then use a plumb line to draw a vertical line downwards and then repeat this from a
second point. The centre of mass is where the lines meet.
What is the principle of moments?
The sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about that same
point for an object in equilibrium.
What is the weight of the second object if two objects are in equilibrium and the first object is 60N with 30m from the
pivot and the second object is 20m from the pivot?
60 x 30 = 180
180/20 = 90N
How is the stability of an object increased?
You can increase the stability of an object by lowering the centre of mass of the object or widening the base.
When will an object tend to topple?
An object will tend to topple when the line of action of its weight is outside its base.
Explain circular motion
For an object that is moving in a circle at a constant speed will be continuously accelerating towards the centre of the circle
and this is because there is always a constant change in velocity which occurs because there is always a constant change in
direction since the object always has to be at a tangent to the circle.
What is a centripetal force?

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An object that is moving in a circle must be acted on by a resultant force that acts towards the centre of the circle and we
say that the resultant force is centripetal because it is centre seeking.
What is gravitational attraction?
Gravity is an attractive force which is increased the greater the mass of each object is and also the smaller the distance
between the two objects is.…read more

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The amplitude of a sound is how loud it is and the pitch of the note depends on the frequency of the sound waves.…read more

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In a step up transformer the secondary has more coils than the primary and in a step down transformer the secondary has
less coils than the primary.
What are the formulas?
P.D across the primary / P.D across the secondary = turns on the primary / turns on the secondary
Primary current x primary voltage = secondary current x secondary voltage
What is the Big Bang?
This created the universe about 13 million years ago.…read more


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