Scalars cannot be negative, but vectors can be, as a certain direction is positive
Displacement is 0 at the height of a cliff, above the cliff the ball has positive displacement, and below the cliff top the ball has negative displacement
In long answer questions, you may be able to decide where the "0" point of a vector may lie
Speed
Velocity when given a direction
A car travelling round a roundabout at constant speed has a constantly changing velocity, therefore it is accelerating
Vectors
Can be represented by arrows, with their size/length representing the vector magnitude
All matter has a gravitational field, and attracts all other matter. The larger the mass, the stronger the field, the greater the attraction
Weight
The force exerted on a mass by the gravitational field, in Newtons. Weight = mass x gravitational field strength
On Earth, the gravitational field strength, g, is 9.8
The acceleration in free fall is due to gravity, and is the same as g, i.e. 10m/s^2
The weight of an object is considered to act at the object's centre of mass
Resultant force
A single force representing the sum of all the forces acting on an object
Skydiver example
1. Initially, only weight acts
2. As he falls, air resistance increases, resultant force decreases
3. Eventually air resistance equals weight, so no resultant force and he reaches terminal velocity
Free body diagram
Shows the forces (and their directions) acting on an object
Resolving forces
A force F at angle θ to the ground can be resolved parallel and perpendicular to the ground using Pythagoras' Theorem
Work
Work Done = Force x Distance
One joule of work is done when a force of one newton causes a displacement of one metre
Work done against frictional forces causes a rise in temperature of the object
Deformation
Changing the shape of an object
Types of deformation
Elastic (object returns to original shape)
Plastic (object does not return to original shape)
Hooke's Law
The extension of an elastic object is directly proportional to the force applied, provided the limit of proportionality is not exceeded
Work done on a spring
Work Done = 1/2 kx^2, where k is the spring constant and x is the extension
Moment of a force
Moment = Force x Perpendicular distance from pivot
Equilibrium is when the sum of anticlockwise moments equals the sum of clockwise moments
Gears
Can change speed, force or direction by rotation
If connected to a smaller gear, the second gear will turn faster but with less force, in the opposite direction
If connected to a larger gear, the second gear will turn slower but with more force, in the opposite direction
Pressure
Pressure = Force/Area
Pressure in a fluid
Pressure in a liquid varies with depth and density, leading to an upwards buoyancy force
The atmosphere gets less dense with increasing altitude
The weight of the air is the force which causes atmospheric pressure
Upthrust
A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface, creating a resultant force upwards
Earth's Atmosphere
A thin layer (relative to size of the earth) of air around the Earth
The atmosphere gets less dense with increasing altitude
The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth. The atmosphere gets less dense with increasing altitude.
Idealised Assumptions, for a simple model of the atmosphere
Isothermal, so it is all at the same temperature
Transparent to solar radiation
Opaque to terrestrial radiation
Distance
How far an object moves, does not involve direction, a scalar quantity
Displacement
Includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line, a vector quantity