1Define force
A push or a pull
2Three things forces can change
Speed
Direction
Shape of a body
3Examples of contact forces
Friction
Air resistance
Tension
Reaction (normal) forces
4Examples of non-contact forces
Weight
Electrostatic forces
Magnetic fields
5Describe friction
A force that opposes motion
Occurs when objects rub against each other
6Describe air resistance
A type of friction force
Occurs when an object moves through air
7Describe tension
A force that pulls two connected objects (by a length of string or rope)
8Describe reaction or normal force
Force that pushes objects apart
Occurs when objects are supported by a surface
9Describe gravitational attraction
Attractive force between two objects with mass
10Describe electrostatic force
An attractive or repulsive force between two charged objects
11Describe magnetic force
An attractive or repulsive force between magnetic poles
12Examples of rotation caused by forces
A child on a see-saw
Turning the handle on a spanner
A door opening and closing
13Define moment
The turning effect of a force
14Moment equation
Moment (Nm) = Force (N) x perpendicular distance (m)
M = F x d
[Diagram showing perpendicular distance]
15Moments when an object is in equilibrium
Sum of the clockwise moments = Sum of the anticlockwise moments
16If an object is balanced…
Sum of the clockwise moments = Sum of the anticlockwise moments
17How are levers and gear systems useful?
They transmit and amplify the rotational effects of forces
18How can you make a lever work better?
Increase the size of the force
Increase the perpendicular distance of the force from the pivot
19If a smaller gear drives a larger gear…
Force will be the same on both gears.
The larger gear will rotate slower but will have a greater moment
20If a larger gear drives a smaller gear…
Force will be the same on both gears.
The smaller wheel will rotate faster but will have a smaller moment
21How can you reduce unwanted energy transfers in gears and simple levers?
Use lubrication to reduce friction
Less thermal energy is dissipated to the surroundings