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1.2.3Kinematics

Acceleration — AP PHYSICS 1 Revision Notes & Topical Questions

5 min read 9 parts Lesson 8 of 14 1 quiz

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Lesson summary

1.2.3 Acceleration — AP PHYSICS 1 notes: Define acceleration and calculate average acceleration, interpreting its sign.Acceleration — the rate of change of velocity; a vectorAny change in velocity — a change in speed, direction or both is an accelerationAverage acceleration — aav…

  • Instantaneous acceleration
  • Sign meaning
  • Speeding up or slowing down
  • At the top
  • Coming down
  • Car from rest

Part 1 of 7Definition

Acceleration
  • Acceleration the rate of change of velocity; a vector
Any change in velocity
  • Any change in velocity a change in speed, direction or both is an acceleration

Part 2 of 7Average and instantaneous

Average and instantaneous
Average acceleration
  • Average acceleration aavg = Δv/Δt = (v − v0)/t
Instantaneous acceleration
  • Instantaneous acceleration acceleration at one moment, found from a very small interval
Example
  • Example a train from rest to 50 m s-1 in 60 s has aavg = 0.83 m s-2

Part 3 of 7Sign of acceleration

1Sign meaning
  • Sign meaning gives only the direction of the acceleration vector
2Speeding up or slowing down
  • Speeding up or slowing down depends on whether acceleration and velocity have the same or opposite sign

Part 4 of 7Ball thrown vertically

Going up
  • Going up velocity upward and decreasing in magnitude
At the top
  • At the top speed is zero for an instant
Coming down
  • Coming down velocity downward and increasing in magnitude
Acceleration
  • Acceleration constant, downward, equal to g
    • (air resistance ignored)

Part 5 of 7Calculation

Calculation
List the known quantities: aavg, t and v0.
Write v = v0 + aavgt.
Substitute to find the unknown.

Part 6 of 7Pattern

Car from rest
  • Car from rest a = 7.1 m s-2 for 3.7 s
Result
  • Result v = 0 + 7.1 × 3.7 = 26 m s-1

Part 7 of 7More from the specification

More from the specification
Displacement
  • Change in position.
Distance
  • Total length of path travelled, a scalar.
Speedometer
  • A device showing the instantaneous speed of a vehicle.
Coordinate system
  • Perpendicular axes used to resolve forces.

Key terms

TermMeaning
AccelerationRate of change of velocity.
Average accelerationChange in velocity over a time interval.
Free fallMotion under gravity alone.
m s-2Unit of acceleration.

Avoid these mistakes

Avoid these mistakes
Saying negative acceleration means slowing down.
Saying zero velocity means zero acceleration.
Forgetting that direction changes are accelerations.

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