Distance & Displacement
- Distance is a scalar quantity - it has size only
- Displacement is a vector quantity, and is distance in a certain direction - it has size and direction
The distance between Coleraine and Belfast is roughly 75km.
The displacement between Coleraine and Belfast is 75km SE. The displacement from Coleraine to Belfast to Coleraine again, though is 0km.
Displacement is represented by an arrow. The length of the arrow is proportional to the distance and the direction of the arrow is in the same direction as the displacement
Speed & Velocity
- Speed is a scalar quantity - it has size only
- Velocity is a vector quantity - it has size and direction
Speed is a distance travelled in unit time - eg. m/s, km/h.
Velocity is a distance travelled in unit time in a specific direction or...
Velocity is a displacement travelled in unit time - eg. m/s due S, km/h due NW.
Average Speed and Acceleration
To find the average speed an object is going, you take the total distance and divide it by the time taken:
- When the velocity of a body increases or decreases, we say it is accelerating
Acceleration is defined as the change in velocity per unit time.
A positive acceleration means that the velocity is increasing.
A negative acceleration (deceleration) means that the velocity is decreasing.
- The distance is on the y axis, against the time on the x axis
- The slope gives you the speed
- The greater the slope, the greater the speed
- A horizontal line means the object is stationary
Velocity -Time Graphs
- The velocity is on the y axis against the time on the x axis
- The slope of the graph gives you the acceleration
- A horizontal line means that the object is travelling at a constant velocity; acceleration=0
- The area under the velocity-time graph represents the total displacement travelled