P1. Motion

Speed

• Speed= distance/time
• The speed of an object is the distance it travels per unit time. We quantify this as the ratio of the distance it travels to the time taken to travel that distance.
• The formula for speed is above and the units are ms-1 or m/s.
• Ex. Michael runs a marathon. He runs 40km in 2 hours. What is his average speed?Well, the distance Michael travels is 40km. He does this in 2 hours. Therefore, using the formula Speed= Distance/Time, we get:
• Speed = 40 km / 2 hours
• Speed = 20 km / hour

Distinguish between speed and velocity

• Basically, speed and velocity are both different type of quantities. The two types of quantities are:
• Vector
• Scalar
• Vector quantities have both a magnitude and direction. Scalar quantities only have a magnitude but no direction. That is the fundamental difference between velocity and speed. Velocity is a vector whilst speed is a scalar. Velocity not only measures how fast something travels, but also the direction it is traveling in, something the speed neglects.

Graphs

• SPEED/TIME GRAPH
• Green line: Constant acceleration.
• Orange Line: If you look at the y-axis, speed doesn’t change, so we can say the object is travelling with a constant speed.
• Blue line: Object is now decelerating, in which change in velocity is now a negative value.
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Folie 4

• DISTANCE/TIME GRAPH
• Green line: Speed of the object is constant, and can be found by dividing Distance by Time. We can tell speed is positive as both time and distance travelled are also both positive.
• Orange line: Distance is not changing so object remains stationary with no movement.
• Blue line: Steady speed returning to the start.
• The red line is steeper than the green line, so therefore it is travelling at a faster speed. Steepness is basically a measure of the gradient of the Distance/Time graph, which is also the speed of an object. The steeper the graph, the higher the gradient, and therefore the faster the speed.
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