2.1.1 Define displacement, velocity, speed and acceleration.
Quantity | Definition | Type |
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Displacement | Distance moved in particular direction | Vector |
Velocity | Rate of change of displacement | Vector |
Acceleration | Rate of change of velocity | Vector |
Speed | Rate of change of distance | Scalar |
2.1.2 Explain the difference between instantaneous and average values of speed, velocity and acceleration.
- Instantaneous speed, velocity or acceleration are quantities at certain points in time (ie. 2 seconds).
- Average quantities include all values at all points within a certain timeframe (ie. from 0 to 10 seconds).
If you cover 240km in 3 hours, your average speed was 80km/h. While this may be your average speed, it is unlikely that your speed at every instant was 80km/h. The speedometer in your car would give you your instantaneous speed.
2.1.3 Outline the conditions under which the equations for uniformly accelerated motion may be applied.
The equations above can only be used when the acceleration is uniform. This means that the acceleration must remain constant, otherwise the formulas will not work. Such questions will utilize the variables below:
Variable | Symbol |
---|---|
Time | t |
Distance travelled | s |
Initial velocity | u |
Final velocity | v |
Acceleration | a |
2.1.4 Identify the acceleration of a body falling in a vacuum near the Earth's surface with the acceleration g of free fall.
A free fall is when an object falls to the earth's surface without the effects of air resistance. When calculating a free fall, we only take into account the value of acceleration due to gravity: 9.81ms^-2. This value, usually represented as the letter g, can be replaced with a in the above formulae when appropriate.
2.1.5 Solve problems involving the equations of uniformly accelerated motion.
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2.1.6 Describe the effects of air resistance on falling objects.
Air resistance will affect all objects in motion. When an object falls from the sky, air resistance will act upon it and create a force that goes in the opposite direction of gravity. These two contradicting forces will eventually cause the object to reach a "terminal velocity". This is a constant velocity, meaning that there is no longer any acceleration present. Without air resistance, the object would continue to accelerate until it reaches the ground. The faster an object falls, the greater its air resistance. Heavier objects take a longer time to reach their terminal velocity.
2.1.7 Draw and analyze distance-time graphs, displacement-time graphs, velocity-time graphs and acceleration-time graphs.
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2.1.8 Calculate and interpret the gradients of displacement-time graphs and velocity-time graphs, and the areas under velocity-time graphs and acceleration-time graphs.
Displacement
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Velocity
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Acceleration
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2.1.9 Determine the relative velocity in one and in two dimensions.
If you are sitting in your room at the moment, your velocity would be 0m/s relative to the room. However, if your room were on the equator, your speed relative to space would be 1700km/h. All motion is relative. Usually, motion will be calculated relative to the earth unless otherwise stated. This is called an "inertial reference" (in this case, the earth).