1.1 Mechanics Notes

Units of Speed

Speed is calculated using both time and distance. Before you can answer questions about speed, you need to understand these variables.    Speed = distance travelled over a period of time (metres per second, kms per hours etc.)   Velocity = speed with direction. 

Converting Units Image (binary/octet-stream)

Calculating Speed

Speed is a measure of how far an object can travel in a certain amount of time. We often use kilometres per hour in everyday life. However, scientists generally use metres per secondas it is a more useful measure of speed. To calculate speed, we need to know two variables: distance travelled and time taken to travel that distance.    To calculate speed, scientists use the formula: Speed (v) = d (change in distance)                                                                            ____________________                         t (change in time) Velocity Equation  v = velocity - speed with direction (ms-1 or m/s) d = distance (m)  t = time (s)   

Formula Triangesl (binary/octet-stream)

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Examples

A turtle travels 2 metres in 300 seconds. What speed is it travelling?  v = d/t v = 2m/300s v = 0.007 m/s   A 747 travels from L.A. to Auckland at 700km/hr. The trip takes 9 hours. How far has the plane travelled? (answer in km then convert to m)  d = v x t d = 700km/hr x 9hrs d = 6,300km  d = 6,300,000m   A train travels from Wellington to Auckland at an average speed of 110km/hr. The distance it covers is 550km. How long does the trip take? (give your answer in hr convert to secs)  t = d/v t = 550km/110kmhr t = 5 hrs t = 18,000 secs  

Distance Time Graphs

Describing the motion of an object is occasionally hard to do with words. Sometimes graphs help make motion easier to picture, and therefore understand.