# P4 - Explaining motion

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• P4 - Explaining Motion
• Speed and Velocity
• Speed tells you how far an object will travel in a certain. It does not tell you the direction of travel
• Velocity tells you how far an object will travel and also its direction of travel
• Speed-Time graphs
• The slope represents the acceleration of the object. The steeper the slope, the greater the acceleration
• Velocity-Time graphs
• A velocity-time graph shows how the velocity, at which an object is moving, changes with time
• Terminal velocity is when one force is equal to another. The resultant force is 0 and the speed becomes constant
• As a skydiver jumps , he initially accelerates due to gravity, but as the jump goes on, air resistance equals the force of gravity. This means that the resultant force is 0 and he falls at a constant speed.
• Distance-Time graphs
• The slope/gradient on the graph shows:
• The speed of the object. The steeper the slope, the greater the gradien
• A distance-time graph shows how the distance traveled by an object changes with time
• Acceleration
• To calculate acceleration you need to use the formula:
• Acceleration (m/s^2) = Change in velocity (m/s) / Time taken for change (s)
• The acceleration of an object is the rate at which its velocity changes
• Deceleration is simply put, negative accelereation
• Forces
• Momentum
• To calculate momentum you need the formula:
• Momentum (kg m/s) = Mass (kg) / Velocity (m/s)
• To calculate change in momentum you need the formula:
• Change in momentum (kg m/s) = Resultant force (N) / Time the force for (s)
• A force occurs when two objects interact with each other
• Whenever one object exerts a force on another, it always experiences an equal yet opposite force in return
• For example: A rocket's engines push gas backwards and the gas pushes the rocket forwrds
• Friction
• When two objects try to slide past each other both objects experience a force that tries to stop them moving. This is friction
• A moving object experiences friction but so do non moving objects.
• For example: A car parked on a slope is trying to roll down the hill due to gravity. But there is enough friction from the brakes to stop it
• Speed-Time graphs
• The slope represents the acceleration of the object. The steeper the slope, the greater the acceleration
• A moving object experiences friction but so do non moving objects.
• For example: A car parked on a slope is trying to roll down the hill due to gravity. But there is enough friction from the brakes to stop it

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