Motion Flashcards
What is displacement?
Distance in a given direction
What is speed?
Change of distance per unit time
What is velocity?
Change in displacement per unit time. or speed in a given direction.
Between speed, velocity and displacement, distance which are vectors or scalar?
Speed and distance are scalar quantities. Velocity and displacement are vector quantities.
What is the unit for speed and velocity?
ms-1
For example, a car travelling at a speed of 30 ms
−1 on a motorway travels a distance of
30 m every second.
How many meter in every minute?
What about in 1 hour?
Convert 30 ms
−1
to kmh−1?
1800 m every minute.
In 1 hour, the car would therefore travel a distance of 108000m or 108km
30 ms
−1 = 108 kmh−1
.
What is the equation for speed?
For an object which travels distance s in time t at constant speed.
Speed 𝑣 = s/t
Distance travelled 𝑠 = 𝑣t
What is the equation for an object moving at constant speed on a circle of radius r,
𝑣 =
2𝜋𝑟/T
where T is the time to move round once and 2𝜋𝑟 is the circumference of the circle
What is the equation for average speed?
𝑣 = ∆𝑠/∆t
What is the graph of an object moving at constant speed on a distance-time graph?
a straight line
with a constant gradient.
What is the graph of an object moving at changing speed on a distance-time graph?
The gradient of the graph changes so the speed of the object is calculated as distance travelled/time taken
How is speed calculated on a distance-tie graph?
The gradient of the line i.e distance travelled/ time taken
Can an object moving at constant velocity move at the same speed when changing direction?
An object moving at constant velocity moves at the same speed without changing
its direction of motion.
If an object changes its direction of motion or its speed or both, its velocity changes.
For example, the velocity of an object moving on a circular path at constant speed
changes continuously because its direction of motion changes continuously
What is Acceleration?
Change of velocity per unit time (ms-2). It is a vector
What is uniform acceleration?
The velocity of an object moving along a straight line changes at a constant rate. This is when acceleration is constant.
What is is the equation to calculate acceleration
𝑎 = (𝑣 − 𝑢)/t
What is non-uniform acceleration?
the direction of motion of an object changes, or its speed changes, at a
varying rate.
What is the gradient of a velocity-time graph used to calculate?
Non uniform acceleration.
What are the 4 suvat equations?
- 𝒗 = 𝒖 + 𝒂𝒕
- 𝒔 = ((𝒖+𝒗) 𝒕)/2
- 𝒔 = 𝒖𝒕 + 0.5𝒂𝒕^𝟐
- 𝒗^𝟐= 𝒖^𝟐 + 𝟐𝒂s
How can you find displacement using a velocity-time graph?
- If at constant velocity: The area under the line between the start and time t since displacement = v x t
2: If at constant acceleration: since 𝒔 = ((𝒖+𝒗) 𝒕)/2 then displacement is the area under the line between start and time t, calculated as a triangle
- Changing acceleration: the area under the line where v represent the velocity at time t and v + 𝛿v represent the velocity a short time
later at t + 𝛿t . (𝛿 is pronounced ‘delta’.)
Because the velocity change 𝛿v is small compared with the velocity v, the displacement
𝛿s in the short time interval 𝛿t is v𝛿𝑡.
This is represented on the graph by the area of the shaded strip under the line, which
has a base corresponding to 𝛿t and a height corresponding to v. In other words,𝛿𝑠= v𝛿t
is represented by the area of this strip
What is the acceleration of freefall?
The acceleration of freefall is the constant acceleration of a free falling object denoted by g. It is equal to 9.81ms^-2
Can suvat be used in freefall situations?
Only when air resistance is negligible
How should freefall values be entered into suvat equations?
+ for items thrown upwards, - for falling downwards.
Describe a Displacement time graph
for on object projected upwards
- Immediately after leaving the thrower’s hand, the velocity is
positive and large, so the gradient is positive and large. - As the ball rises, its velocity decreases so the gradient decreases.
- At maximum height. its velocity is zero, so the gradient is zero.
- As the ball descends, its velocity becomes increasingly negative,
corresponding to increasing speed in a downward direction.
So the gradient becomes increasingly negative It looks like an upside down U