Speed is measured in km/h (kilometers per hour)
It is a measure of the time it takes an object takes to move from one loaction to another over a set distance
Speed = distance / time
If an object is traveling at the same speed for aperiod of time (highly unlikely) then it is called a constant speed.
If a car changes speed from slow to fast, it is called acceleration.
If a car slows down, it is called deceleration.
Velocity is the speed and direction that an object is traveling.
Velocity can be both possitive and negative. eg if a car travels north for 3 miles then it is a 'possitive velocity' but if the car travels back south down the same road for 2km it is 'negative velocity'.
The gradient of a velocity-time graph is equal to the acceleration and flat sections represent a constant speed. Also a curve represents a change in acceleration.
A force occurs when two objects interact. eg. A person pushing a wall. The two objects are called interaction pairs.
The theory behind interaction pairs is stated in Newton's Third Law:
All actions have an equal and opposite reactions meaning if object 1 pushes against object 2, then object 2 exerts an equal force in an opposite direction to object 1.
All moving objects experience friction whether it is between two solid surfaces gripping onto each other (static friction), sliding past each other or the resistance from gas or liquid (drag)