1. Forces & Motion

• momentum is the measure of how hard it is to stop something
• acceleration is the rate of change of an objects velocity
• air resistance is the frictional force on an object moving through the air
• average speed is the speed calculated from total distance travelled divided by total time taken
• the centre of mass is the point at which the mass of an object can be considered to be concentrated
• the average velocity of the toy car is given by the distance moved divided by the time taken
• In a distance time graph a straight line represents constant speed
• in a distance time graph a very steep slope means the object is moving at a large speed
• in a distance time graph a shallow slope means the object is moving at a small speed
• in a distance time graph a flat, horizontal line means the object is stationary (not moving)
• In a distance time graph an objects might be moving at a changing speed, this is represented by a curve
• in a distance time graph if the slope is increasing, the speed is increasing (accelerating)
• in a distance time graph if the slope is decreasing, the speed is decreasing (decelerating)
• The speed of an object is the distance it travels every second
• Speed is a scalar quantity. This is because it only contains a magnitude (without a direction)
• Acceleration is defined as the rate of change of velocity. In other words, it describes how much an object's velocity changes every second
• acceleration = change in velocity/time taken
• The change in velocity is found by the difference between the initial and final velocity
• An object that speeds up is accelerating
• An object that slows down is decelerating
• The acceleration of an object can be positive or negative, depending on whether the object is speeding up or slowing down
• If an object is speeding up, its acceleration is positive
• If an object is slowing down, its acceleration is negative 
• velocity time graphs show if the object is moving with a constant acceleration/deceleration and the magnitude of the acceleration/deceleration
• in a velocity time graph a straight line represents constant acceleration
• In a velocity time graph the slope of the line represents the magnitude of acceleration. A steep slope means large acceleration 
• In a velocity time graph a gentle slope means small acceleration
• The area under a velocity-time graph represents the displacement
• If the area beneath the graph forms a triangle then the area can be determined by using the following formula: Area = ½ × Base × Height
• Enclosed areas under velocity-time graphs represent total displacement 
• The following equation of motion applies to objects moving with uniform (constant) acceleration:

  (final speed)2 = (initial speed)2 + 2 × acceleration × distance moved
• Changes in speed: forces can cause bodies to speed up or slow down
• Changes in direction: forces can cause bodies to change their direction of travel
• Changes in shape: forces can cause bodies to stretch, compress, or deform
• Gravitational (or weight) - the force between any two objects with mass (like the Earth and the Moon)
• Electrostatic - the force between any two objects with charge (like a proton and an electron)
• Thrust the force pushing a vehicle (like the push from rocket engines on the shuttle)
• Upthrust the upward force on any object in a fluid (like a boat on the surface of a river)
• Air resistance (or drag) - the force of friction between objects falling through the air (like a skydiver in freefall)
• Compression forces that squeeze an object (like squeezing a spring)