Unit 1.2:Kinematics Flashcards
Define Displacement
The distance an object travels in any given direction (positive or negative)
Define velocity
The rate of change of displacement
Define speed
Distance traveled per unit time
Define Acceleration
Rate of change of velocity
What 2 words are applied to both speed and velocity?
Mean and instantaneous
What is the ‘mean’ speed/velocity?
The average measured over a significant amount of time
What is ‘instantaneous’ speed/velocity?
The speed or velocity at any given instant
How is mean speed calculated?
v-u/t
How is instantaneous speed calculated?
Taking a tangent to the curve on a displacement-time graph or by taking a very small time interval.
On a displacement-time graph, what is the gradient equal to?
The gradient is equal to the velocity
On a velocity-time graph, what does the gradient represent?
Acceleration
On a velocity-time graph, what is the area under the graph equal to?
The distance travelled
State the 4 kinematic equations
Derive the 4 kinematic equations
How is terminal velocity achieved?
When the air resistance becomes equal to the weight
On a displacement-time graph, what is the gradient equal to?
The gradient of the graph at any point is equal to the instantaneous velocity at that point.
On a displacement-time graph, how do you calculate the average velocity?
Δx/t
On a velocity-time graph, what does the gradient represent?
Acceleration
On a velocity-time graph, what is the area under the graph equal to?
The distance travelled
Derive v=u+at
Use of a= Δv/t
Derive x=(v+u/2)t
Use of Vav=Distance/time and re-arrange
Derive x=ut+½at²
Substitute v=u+at for v in x=(v+u/2)t
Derive v²=u²+2ax
Re-arrange x=(v+u/2)t for t, and substitute t in V=u+at
When air resistance is taken into account, does acceleration remain a constant?
No. When acceleration is taken into account, acceleration becomes non-uniform, and reduces to zero as the object gains speed
Describe how a skydiver reaches terminal velocity.
At the beginning, the sky diver’s vertical speed is zero (or very close to zero), and hence there’s no air resistance.
There’s therefore a downward resultant force created by the weight. This causes the skydiver to accelerate downwards. As the skydiver’s speed increases, he/she pushes downwards on the air molecules with an
increasing force, since the air’s momentum is changing at a greater rate. Hence the air molecules, by newton’s 3rd law, are creating an upward force on the skydiver
(air resistance) that increases with speed.
Eventually, the air resistance becomes equal to the weight, and terminal velocity is reached.
