# Forces and Motion

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• Created by: Eesha Dev
• Created on: 27-03-16 12:37

The Difference Between Speed, Velocity and Acceleration

Speed is the distance an object travels during a specific period of time. We can use units like m/s or km/hr. Velocity is the speed in a given direction and to give the velocity of a body, you need to state both its speed and the direction that it travelled in. You can use an arrow, a compass direction or a + or - sign. Acceleration is the rate at which the velocity changes. Something is accelerating when its velocity is changing. A body that is slowing down ia decelerating. This means that it has negative acceleration and if something decelerates at -3m/s² it means that the velocity is going down by 3m/s every second.

How to Work Out Speed

How to Work Out Acceleration

Distance-Time Graphs

A distance time graph can be used to describe and work out the speed of an object. The slope of a distance time graph gives the speed from the gradient and when something is stationary, the line is horizontal. A steeper line means a faster speed.

Velocity-Time Graphs

A velocity-time graph can be used to describe the velocity and acceleration of an object. For these graphs, a horizontal line means that the object is moving with a constant velocity but if the line is straight and diagonal, it means that the object is moving with a contant acceleration (since the velocity is changing) - Remember how to calculate acceleration.

Here, the gradient of the line gives the acceleration

How to Calculate Distance Using Graphs

The area below the graph line in a velocity-time graph represents the distance travelled.

How do Forces Affect the Movement of a Body?

Forces have size and direction and it is shown by using an arrow. The arrow shows direction while its length shows the size of the force. To make a trolley move, you have to push it to move it forward and pull it to move it backwards. Whatever the direction of the force you exert, the trolley always exerts an equal sized force onto you in the opposite direction. This is because forces come in pairs and you can't have one without the other. Whenever two things interact, the forces they exert on each other are always equal in size and opposite in direction

Resultant Force

The resultant force is a single force that has the same effect on something as all the original forces acting together. If two forces are opposite in direction and equal in size, they are balanced and therefore does not accelerate. It remains at rest or continues in the same speed and direction. If the two forces are not equal in size, it is unbalanced and the difference between them is the resultant force.

Newton's First Law

An object will continue with the same velocity unless acted on by a resultant force (unbalanced forces). If the forces were balanced, then the onject would continue with the same velocity since the…