Motion Flashcards
What is displacement?
The shortest distance from the initial to the final position of an object.
It is a vector quantity.
Sign determines the direction.
What is instantaneous speed?
The speed at any instant, can be measured by a speedometer.
What is velocity?
Rate of change of displacement with respect to time.
It is a vector quantity.
Magnitude of the velocity is speed.
What is acceleration?
Rate of change of velocity with respect to time.
When is a object undergoing uniform acceleration?
When there is a constant change in velocity per unit time.
Where else can an object undergo acceleration?
When it is changing direction, because its velocity has changed therefore it has undergone acceleration.
What does the gradient of a d-t graph give you?
Velocity.
If the gradient is steeper then the speed of the object is larger.
If the gradient is constant then the velocity of the object is constant.
If it is horizontal (0 gradient) then the object is stationary.
If the gradient is decreasing then the object is decelerating.
If the gradient is increasing then the object is accelerating.
How do you work out the instantaneous speed at a point on a curved graph?
A tangent is drawn, and the gradient of that is calculated.
What does the gradient of a v-t graph give you?
Acceleration.
If straight line then acceleration is uniform.
Steeper the gradient, the greater the acceleration
Increasing gradient means increasing acceleration
Decreasing gradient means decreasing acceleration.
What does the area under a v-t graph give you?
Displacement.
Areas under any negative parts of the graph count as negative areas, as they show the object moving back to its starting point.
To estimate the area under a curve count the squares.
What is free fall?
The motion of an object undergoing an acceleration of g (9.81 ms^-2).
How do you measure acceleration due to gravity?
- Drop ball bearing from electromagnet.
- Measure distance ball falls, using metre ruler and time of fall using stopwatch (or electronic timer linked to electromagnet and trap-door).
- s = ut + 0.5at^2 and u = 0, therefore g = (2s)/t^2
- Plot graph of s against t^2
- g = 2 * gradient
What is acceleration due to gravity found from the experiment an estimate?
- Drag on ball is ignored
- Reaction time on starting/stopping stopwatch (if used)
- Parallax problems
- Residual magnetism delays release of ball
- Trap door takes time to open
How did Galileo disprove the idea that heavier objects fall faster than lighter ones?
- Dropped two cannonballs with different masses (but same size)
- Dropped from the same height (top of leaning tower of Pisa).
- Hit ground at same time
- Both balls had same acceleration therefore Aristotle was wrong.
What is the definition of a projectile?
A projectile is any object that once projected or dropped continues in motion by its own inertia and is influenced only by the downward force of gravity.
