Motion

Motion

1. Speed & Velocity

   • Speed is SCALAR
     • Speed shows no direction e.g 20mph
     • Scalar measured using a stopwatch
     • Speed varies
       • Calculate it usingDistance/Speed x Time
   • Velocity is VECTOR
     • Velocity uses direction e.g 30mph north
       • Left to Right = positive. Opposite direction = negative.
     • Vector Represented with an arrow (length = magnitude (size) . Direction = direction)
       • You can add vectors but look at the 'sign'
       • e.g +20m/s + +20m/s=+40m/s +20m/s + -20m/s=Zero
   • Estimates
     • Walking - 1.5m/s Running - 3m/s Cycling 6 m/sCar - 25m/s Train - 55 m/s Plane 250 = m/s

2. Measurement of Motion

   • A ruler for distance.
     • Use an Ultrasound for accuracy
       • A timer starts and stops when an object interrupts the light beam
   • A Stop watch for time
     • To get around reaction time for accuracy use a light gate
       • measures the time taken for a pulse to travel there and back. This value and the speed of the pulse used to work out distance
   • Uniform Motion = Speed does not change
     • Distance (m) = Speed (m/s) x Time (s)
   • Non-Uniform Motion = Average speed
     • Average speed (ms) = Total distance (m)/Total Time (s)

3. Distance & Displacement

   • Displacement in a VECTOR
     • It has a start and an end in a straight line
     • Shows Direction
   • Distance is a SCALAR
     • No direction
     • Use a ruler, measuring wheel etc to measure
   • e.g If you walk 5m North then 5m South
     • Displacement = 0m
     • Distance = 10m

4. Acceleration

   • Uniform Accelertion
     • acceleration does not change
       • i.e. Slow down or speed up at a constant rate
   • Acceleration (m/s2) = Change in Velocity (m/s)/Time (s)
     • Rearrange this equation to suite the question
       • If you know the initial and the final velocity then subtract them to find the change in velocity
   • Deceleration = Negative Acceleration i.e. Slowing down
     • Best to say negative acceleration
   • Change in Velocity over a certain period of time
     • The times it takes different cars to hit 60mph
       • If traveling in a straight line the times show changes in speed or acceleration

5. Displacement-Time Graph

   • The gradient can be positive or negative
     • The gradient is the Velocity so shows direction as well as magnitude

6. Distance-Time Graphs

   • A graph shows a 'journey'
     • Distance against time shows the speed
       • The gradient or 'slope' shows the speed. -Straight-line = Constant speed. Horizontal-line = object is not moving. The steeper the line = faster the object is traveling

7. Velocity-Time Graph

   • Rate of change of velocity to show acceleration
     • For a falling object = downwards is positive
       • For a ball that goes up and down = shows positive and negative values
         • Distance travelled is the area under the speed-time graph
           • Find the area using squares or rectangles or by counting squares. Multiple speed by time to get distance