Motion and energy
Speed velocity and acceleration
- Speed
- Average speed= distance moved / time taken
- Velocity
- Speed is a distance travelled in unit time ( scalar )
- Velocity is a distance travelled in unit time in a stated direction ( vector )
- Velocity = distance moved in a stated direction / time taken = displacement / time
- Velocity of a body is constatnt if it moves with steady speed in a straight line
- Distance moved in a stated direction is also known as displacement
- Acceleration
- It is the change in velocity in unit time
- Acceleration = change of velocity / time taken for change
- An acceleration is positive if the velocity increases and negative if it decreases. A negative acceleration is also called a deceleration or retardation
- Timers
- These are timers used to analyse motion
- Motion sensors
- They use the ultrasonic echo technique to determine the distance of the object from thee sensor
- Tickertape timer : tape charts
- One type has a marker which vibrates 50 times a second and makes dots at 1/50 s intervals on the paper tape being pulled through it
- 1/50 s is called a tick
- The distance between the successive dots equals the average speed of the object
- 1/5 s is called a tentick
- 5 tenticks = 1 second
- Photogate timer
- They are used to record time taken for a trolley to pass through a gate. If the length of the interrupt card is measured, the velocity can be calculated
Graphs and equations
- Velocity – time graphs
- Tape charts are velocity – time graphs which show the velocity changing in jums rather than smoothly.
- Motion sensors give a smoother plot
- The area under this graph measures the distance moved
- The slope or gradient of a velocity time graph shows the acceleration of a body