adminWhat are Distance, Displacement, Speed and Velocity?
1. What is Distance?
Distance is a measure of how far an object has travelled from its starting point, or how far away it is.
Distance is the same as length and is measured in metres.
2. What is the Difference between Distance and Displacement?
Displacement (like distance above) is also a measure of how far an object has travelled from its starting point but displacement also tells you the direction of the object.
Distance is a scalar and displacement is a vector.
3. What is Speed?
Speed is a measure of how fast an object is moving.
It is measured in metres per second, written as m/s.
Speed = Distance ÷ Time.
4. What is Velocity?
Velocity is similar to speed.
It is also a measure of how fast an object is moving and is measured in m/s.
Velocity = Distance ÷ Time.
If an object is not moving then it is called stationary.
The speed or velocity of a stationary object is zero.
5. What is the Difference between Velocity and Speed?
The difference between velocity and speed is that velocity is speed in a certain direction.
Speed is a scalar and velocity is a vector.
If an object is moving in a straight line, then its speed and velocity will be the same.
If the moving object stays at the same speed but changes direction then we say that the velocity has changed (because the direction has changed) but the speed has stayed the same.
If the velocity in one direction is positive (for example, forwards at 10 m/s) then the velocity in the opposite direction is negative (for example, backwards at -10 m/s).
In most of the examples of motion that you will come across, the object will be moving in a straight line.
In this case, we will use the word velocity rather than speed
6. How is the Velocity of an Object Calculated?
Either Speed or Velocity = Distance ÷ Time.
For example, if an object moving in a straight line travels 25 metres in 5 seconds, then its velocity = 25 ÷ 5
= 5 m/s.
You must always say what the units are!
(in this case m/s, called “metres per second”).
Always check what units are given in the question.
If the time is given in hours or minutes, then convert it to seconds before doing the calculation.
7. What is Constant Velocity?
If an objects velocity does not change, we say that it has a constant velocity.
In the above example, we are not told whether the object has a constant velocity, or whether its velocity has changed during the 5 seconds.
If the velocity has changed, then the answer we have calculated is an average velocity of 5 m/s.
If the velocity has not changed, then the object had a constant velocity of 5 m/s.
8. What is Acceleration?
A change in velocity is called acceleration.
9. What is the Equation for Acceleration?
Acceleration = Change in Velocity ÷ Time.
This equation is written as
a = (v-u) ÷ t
where a = acceleration
v = final velocity (the one it ended up with)
u = initial velocity (the one it started with)
t = time
This equation is important!
10. What are the Units of Acceleration?
The units of acceleration are m/s2 called “metres per second squared”.
11. What is Negative Acceleration?
If an object gets faster, it will have a positive acceleration.
If an object gets slower, it will have a negative acceleration (this is sometimes called “deceleration” but the term “negative acceleration” is preferred).
12. How is the Acceleration of an Object Calculated?
Acceleration = Change in Velocity ÷ Time.
a = (v-u) ÷ t
where a = acceleration
v = final velocity (the one it ended up with)
u = initial velocity (the one it started with)
t = time
This equation can be rearranged.
Example 1. If a car changes from 10m/s to 30m/s in 8 seconds, what is its acceleration?
v = 30
u = 10
t = 8
a = (30 – 10) ÷ 8
= 20 ÷ 8
= 2·5 m/s2
Example 2. If a bicycle moving at 15 m/s takes 10 seconds to stop, what is its acceleration?
In this example, the final velocity is zero because the bicycle has stopped.
v = 0
u = 15
t = 10
a = (0 – 15) ÷ 10
= -15 ÷ 10
= -1·5 m/s2
The acceleration is negative because the bicycle has slowed down. — gcsescience.com
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