Physics: Energy and Motion
Speed
● Speed: how fast an object is travelling (simply)
● Speed: rate of change of distance (scientifically)
● Speed given symbol v, v is for velocity
● Velocity is speed in a given direction
● Usually measured in meters/ second (m/s) or can use
kilometres/ hour (km/hr) in everyday life
● Average speed= distance travelled / time taken (V=d/t)
● Average speed (given 2 speeds): V ave= V+ U/2 (V= final
speed, U= initial speed)
● Convert m/s to km/hr -- multiply by 3.6
● Convert km/hr to m/s -- divide by 3.6
● Because 1 m/s = 1/1000 km/s = 60 x60/ 1000 km/hr = 3.6 km/hr
● Speed is a scalar quantity. This means that it has a magnitude (size), but no
direction - it's just a number. Distance, another scalar quantity, to calculate
speed.
● Velocity is a vector quantity. This means it has a magnitude (size) AND a
direction. Therefore, use displacement (the vector form of distance) to calculate
velocity.
Distance / Time Graphs
● X axis: time
● Y axis: distance
● Straight slope = constant speed
● Horizontal = not moving
● Speed can be calculated by d/t or rise over
run (gradient)
● Curve indicates a changing speed
(accelerating)
● Speed can be estimated in a curve by
drawing a line at a tangent to a point,
making a right angle triangle and then
following rise/ run method
Speed
● Speed: how fast an object is travelling (simply)
● Speed: rate of change of distance (scientifically)
● Speed given symbol v, v is for velocity
● Velocity is speed in a given direction
● Usually measured in meters/ second (m/s) or can use
kilometres/ hour (km/hr) in everyday life
● Average speed= distance travelled / time taken (V=d/t)
● Average speed (given 2 speeds): V ave= V+ U/2 (V= final
speed, U= initial speed)
● Convert m/s to km/hr -- multiply by 3.6
● Convert km/hr to m/s -- divide by 3.6
● Because 1 m/s = 1/1000 km/s = 60 x60/ 1000 km/hr = 3.6 km/hr
● Speed is a scalar quantity. This means that it has a magnitude (size), but no
direction - it's just a number. Distance, another scalar quantity, to calculate
speed.
● Velocity is a vector quantity. This means it has a magnitude (size) AND a
direction. Therefore, use displacement (the vector form of distance) to calculate
velocity.
Distance / Time Graphs
● X axis: time
● Y axis: distance
● Straight slope = constant speed
● Horizontal = not moving
● Speed can be calculated by d/t or rise over
run (gradient)
● Curve indicates a changing speed
(accelerating)
● Speed can be estimated in a curve by
drawing a line at a tangent to a point,
making a right angle triangle and then
following rise/ run method
