Theme 2: Balancing Forces
Nature and properties of forces
Newton's pairs of forces
Force applied at a distance from a fulcrum
Force applied to a helical spring
Bodies in equilibrium
Moments
Pressure
Atmospheric Pressure
Push or pull
Measured in Newtons using a Newton balance
Mass does not change. Weight is the force produced by the gravitational pull.
Vectors: have both direction and magnitude
Friction is the force which opposes motion
Acts when an object moves through a medium (air/water)/surfaces slide past each other
Weight = mass x gravitational pull
Thrust & Friction
Weight and Reaction
Weight and Tension
Scalar: has magnitude only
Hooke's Law: the force is directly proportional to the extension provided that the elastic limit is not exceeded
Graph = straight line; elastic limit = curve
Gradient = spring constant
Area under graph = energy stored in spring
Elastic limit: the maximum extent to which a solid can be stretched without permanent alteration of size or shape
Levers
Larger distance from fulcrum = larger turning effect
Larger force = larger turning effect
Smaller distance from fulcrum = smaller turning effect
Moment = force x distance
Tower cranes
Principal of moments
When an object is in equilibrium, its anticlockwise moments are equal to its clockwise moments.
2 conditions
Wide base area, low centre of gravity = high stability
Resultant force = 0
Moments are equal or equal to 0
Small base area, high centre of gravity = low stability
Centre of gravity is always on a horizontal base = neutral stability
Centre of gravity = centre of uniform object
Centre of gravity = widest part of asymmetrical object
Standard Unit = Pa or N/m^2
Pressure is inversely proportional to area; P = F/A
High-heeled shoes
Knives
Pins
Wall foundation
Pressure in a liquid = density x height x gravity
Transmit pressure in all directions, enabling force to be magnified (hydraulic machines).
Deep sea diving/scuba diving
Atmosphere exerts pressure and this decreases while height increases
Drinking from a straw
Vacuum Cleaner
Rubber sucker
Syringe
Gas Laws (for a fixed mass of gas)
Charles's Law: Temperature is directly proportional to volume
Boyle's Law: Pressure is inversely proportional to volume
Pressure Law: Temperature is directly proportional to pressure