P2 1.2 Velocity and Acceleration

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P2 1.2Velocity and Acceleration
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P2 1.2 Velocity and AccelerationLearning
Objectives

• Learning Objectives
• Velocity is speed in a particular direction
• Acceleration is the rate of change of velocity.

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P2 1.2 Starter

• Getting nowhere fast A racing driver completes
  a full circuit of a 3 km racecourse in 90
  seconds. What is his average speed?
• Why isnt he 3 km away from where he started?

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P2 1.2 Speed and Velocity

• Do you remember the equation for speed?
• Now write one for velocity.

Speed (metres per second) Distance
(metres)
Time (seconds)
Velocity (metres per second) Displacement
(metres)
Time (seconds)
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Speed vs. Velocity
Speed is simply how fast you are travelling
Velocity is speed in a given direction
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Velocity-time graphs
80 60 40 20 0




Velocity m/s
T/s
10 20 30 40 50
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Sketching More Graphs

• Sketch a graph of displacement against time to
  show the following motion A bus leaves the bus
  station and travels at a steady speed of 30mph
  for 5 minutes until it stops for 1 minute at the
  edge of town to pick up passengers. It then
  continues its journey at 60mph for 10 minutes. It
  stops for 2 minutes to drop off passengers before
  returning to the bus station at a steady speed of
  45mph.
• EXTENSION Now draw a velocity against time graph
  beneath this, showing the same motion.

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Acceleration

• Acceleration is the rate of change of velocity
• The unit for acceleration is m/s2 or m/s/s.

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Acceleration questions

• A cyclist accelerates from 0 to 10m/s in 5
  seconds. What is her acceleration?
• A ball is dropped and accelerates downwards at a
  rate of 10m/s2 for 12 seconds. How much will the
  balls velocity increase by?
• A car accelerates from 10 to 20m/s with an
  acceleration of 2m/s2. How long did this take?
• A rocket accelerates from 1,000m/s to 5,000m/s in
  2 seconds. What is its acceleration?

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80 60 40 20 0




Velocity m/s
T/s
10 20 30 40 50

1. How fast was the object going after 10 seconds?
2. What is the acceleration from 20 to 30 seconds?
3. What was the deceleration from 30 to 50s?
4. How far did the object travel altogether?

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Rolling, rolling, rolling.

• Three balls of the same size are rolled down the
  same slope. One is iron, one wood and one is a
  football. Which will reach the bottom first?
  Explain your ideas.