Mechanics - Velocity and Acceleration Flashcards
How is AVERAGE SPEED calculated?
Total distance travelled / time taken to travel the distance
v = d/t
UNIT= ms^-1
What is instantaneous speed?
The actual speed at a particular moment. Eg speedometer on car. Find instantaneous speed on a velocity-time graph by reading the y-axis.
What if instantaneous speed does not change?
The speed is constant/uniform/steady. If the speed is constant then the average speed will be the same as the constant speed.
How to calculate speed/acceleration in exam?
- formula used (v = d/t)
- the working showing the numbers in calculation
- answer WITH CORRECT UNITS.
Find speed on distance-velocity graph
The gradient is the speed. So:
- if line is straight and has a gradient, the speed is constant.
- if line is horizontal it means that the object is not moving - stationary.
- a steeper slope means the object has a faster speed because there is more distance travelled in less time.
What is acceleration?
When an object’s speed changes (can be both slowing down and speeding up)
Average acceleration is a measure of how much the speed is change every unit time (sec/min/hr)
The rate at which an object changes velocity.
How to calculate acceleration?
change in speed/change in time
a = change in v/change in t
UNIT = ms^-2
How to find acceleration on graph
The gradient of a speed - time graph is the acceleration.
So:
- a straight positive gradient means constant acceleration
- horizontal line means there is NO ACCELERATION so the object is travelling at a CONSTANT SPEED
- a steeper slope means greater acceleration due to a greater change in speed in a shorter time.
Difference between displacement - time graphs and velocity - time graphs
d/t v/t
Positive gradient: moving away | acceleration
0 gradient: stationary | constant speed (0 a)
Negative gradient: moving back towards start | slowing down
Area under graph: nothing | distance travelled
Gradient: Velocity | acceleration
How to calculate distance travelled on velocity - time graph
The area of the shape under the graph line ALL THE WAY DOWN to the time axis, between any two time values, is the distance that has been travelled during that time period.
Define speed
The distance travelled each second/minute/hour. The rate at which distance changes.
What is velocity
Speed with a direction.
An object moving in the negative direction has a negative velocity.
