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  • Created by: Vicky
  • Created on: 28-11-11 21:43

As fast as you can.

Speed and velocity are both measures in metres per second. Speed is just how fast you are going with no regard to direction. Velocity must always have direction specified e.g. 30 miles per hour north. The distance in a particular direction is called the displacement. Displacement over time equals average velocity. Speed cameras can be used to catch speeding motorists at dangerous accident spots. Lines are painted on a road a certain distance apart to measure the distance travelled by the car. A photo of the car is taken as it passes the first line and a second photo is taken a certain time later. These photos can then be used to measure the distance travelled by the car.

Acceleration is how quickly velocity is changing. The change in velocity can be a change in speed or a change in direction or both. Finishing velocity multiplied by starting velocity over time equals acceleration. Units for acceleration is metres per second squared. Velocity time graph notes. Gradient equals acceleration. Flat sections represent steady speed. The steeper the graph, the greater the acceleration or deceleration. Uphill sections are acceleration and downhill sections are deceleration. The area under any section of the graph is equal to the distance travelled in that time interval. A curve means changing acceleration.

A force is either a push or a pull. There are six forces you are required to know. Gravity always acts straight done and makes all thing accelerate towards the ground at about 10 metres per second squared. Reaction force from a surface, usually acting straight upwards. Thrust due to an engine or rocket speeding something up. Air resistance, drag or friction which will slow the thing down. Lift due to an aeroplane wing. Tension in a rope or cable. There are five different force diagrams. Stationary object where all forces are balanced. The force of gravity is acting downwards which causes a reaction force from the surface pushing upwards. Steady horizontal forces where all forces are balanced. Gravity is acting downwards which causes a reaction force from the surface pushing upwards. Thrust is acting forwards with a force of air resistance acting backwards. To move at a steady speed the forces must be balanced. If there is an unbalanced force then you get acceleration. Steady vertical velocity where all forces are balanced. The force of weight is acting downwards with the force of drag acting upwards. The object would be falling at terminal velocity. Horizontal acceleration where there is unbalanced forces. You only get acceleration with an overall resultant force. The bigger this unbalanced force, the greater the acceleration. The other perpendicular forces are still balanced. Vertical acceleration where there is unbalanced forces. There is the force of gravity acting downwards with a smaller force of drag acting upwards causing downwards acceleration.

If an object has no force propelling it along it will always slow down and stop because of friction. Friction always acts in the opposite direction to


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