Speed and Velocity
Speed = how fast an object is moving.
Instantaneous speed = speed of an object at a particular point in time.
Speed (M/S) = Distance travelled (M) / time taken (S)
Velocity = describes an object's speed and direction
The gradient of a velocity-time graph represents how quickly an object is increasing in speed.
Steeper the slope = faster the speed is increasing
Velocity-time graphs are used in lorry tachographs to make sure that drivers rest regularly and dont exceed speed limits.
Forces = occurs when two objcts interact with each other
Forces in an interatction pair are equal in size and opposite in direction
Gravity = force of attraction between all masses
Air Resistance = air tries to slow an object down
Reaction of the Surface = an object is pulled down onto the surface by gravity and the surface pushes up onto the object with equal force
Friction = the force that tries to stop two objects moving as they slide past one another
Resultant force = overall effect of adding or subtracting forces
The gradient of a distance-time graphs represents the speed of an object.
Steeper the slope = greater the speed
To calculate speed using a distance-time graph
-Take any two points on the gradient
-Read off the distance travelled between these points
-Note the time taken between these points
-Divide the distance by the time
Distance-time Graphs continued
Curvey distance-time graphs = speed of an object is changing
Average speed of a curvy distance-time graph = total distance divided by total time
Gradient steeper than dotted line = object travelling faster than average speed
Gradient less steep than dotted line = object travelling slower than average speed
Momentum = measure of the motion of an object
Momentum (kg m/s) = mass (kg) x velocity (m/s)
Change in momentum (kg m/s) = Resultant force (N) x time for force acts for (s)
Collisions cause a change in momentum
If a change in momentum is spread out over a longer period of time, the resultant force will be smaller.
Increasing time of impact = reduces force of impact
Kinetic energy and change in energy
Kinetic energy = the energy an object has because of its movement. it depends on the mass and velocity of an object.
Kinetic energy (J) = 1/2 x mass (kg) x velocity(squared) (m/s)
Change in energy = work done
Gravitational potentional energy= energy an object has because of its mass and height above earth
Object is dropped = GPE decreases = kinetic energy increases
Change in GPE (J) = weight (N) x vertical height difference (m)
Work is done by a force to move an object resulting in the transfer of energy
work done on an object = object gains energy
work done by an object = object loses energy
Work done by a force (J) = force (N) x distance moved by force (m)