OCR A-Level Physics Chapter 3
Study
What is displacement?
The distance travelled in a particular direction. It's a vector quantity with magnitude and
direction. Measured in meters.
What is instantaneous speed?
The speed at the moment it's measured - speed over an infinitesimal interval of time.
What is average speed?
The rate of change in distance calculated over a complete journey.
What is average velocity?
The change in displacement Δs for a journey divided by the time taken Δt. So Δs/Δt
What is acceleration?
The rate of change of velocity, a vector quantity.
How do you work out average speed from a displacement-time graph?
The total distance over time. So find the total increase and decrease in displacement
and divide it by the time travelled.
How do you find the average velocity from a displacement time graph?
Average velocity = Change in displacement over time. Gradient If the subject comes
back to the origin the average velocity is 0.
What do you need to know for distance time graphs?
They represent the motion of objects. Distance is on the y axis and time is on the x axis.
Gradient is = speed.
Constant speed is a straight line.
How can motion be deduced from a velocity-time graph?
-A straight line with +ve gradient = constant acceleration
-A straight line with 0 gradient = constant velocity + 0 acceleration.
-A straight line with -ve gradient = constant deceleration.
-A curve with a changing gradient = changing acceleration
How do you calculate the distance from a velocity-time graph?
For constant acceleration:
-It's the area underneath the graph. Divide it into shapes to find the area.
For changing acceleration:
-It's still the area underneath the graph but you'll have to count the squares underneath
the graph.
How do you workout the acceleration from a velocity-time graph?
Gradient of the velocity time graph.
What are the equations of motion?
How can the equations of motion be derived?
By drawing a velocity time graph. Plot u,v and t and from their work out the area of a
rectangle, trapezium and the gradient of a line.
What is stopping distance?
The total distance travelled from when the driver 1st sees a reason to stop to when the
vehicle stops.
What is thinking distance?
The distance travelled between the moment you 1st see a hazard and the moment
when you use the break.
Study
What is displacement?
The distance travelled in a particular direction. It's a vector quantity with magnitude and
direction. Measured in meters.
What is instantaneous speed?
The speed at the moment it's measured - speed over an infinitesimal interval of time.
What is average speed?
The rate of change in distance calculated over a complete journey.
What is average velocity?
The change in displacement Δs for a journey divided by the time taken Δt. So Δs/Δt
What is acceleration?
The rate of change of velocity, a vector quantity.
How do you work out average speed from a displacement-time graph?
The total distance over time. So find the total increase and decrease in displacement
and divide it by the time travelled.
How do you find the average velocity from a displacement time graph?
Average velocity = Change in displacement over time. Gradient If the subject comes
back to the origin the average velocity is 0.
What do you need to know for distance time graphs?
They represent the motion of objects. Distance is on the y axis and time is on the x axis.
Gradient is = speed.
Constant speed is a straight line.
How can motion be deduced from a velocity-time graph?
-A straight line with +ve gradient = constant acceleration
-A straight line with 0 gradient = constant velocity + 0 acceleration.
-A straight line with -ve gradient = constant deceleration.
-A curve with a changing gradient = changing acceleration
How do you calculate the distance from a velocity-time graph?
For constant acceleration:
-It's the area underneath the graph. Divide it into shapes to find the area.
For changing acceleration:
-It's still the area underneath the graph but you'll have to count the squares underneath
the graph.
How do you workout the acceleration from a velocity-time graph?
Gradient of the velocity time graph.
What are the equations of motion?
How can the equations of motion be derived?
By drawing a velocity time graph. Plot u,v and t and from their work out the area of a
rectangle, trapezium and the gradient of a line.
What is stopping distance?
The total distance travelled from when the driver 1st sees a reason to stop to when the
vehicle stops.
What is thinking distance?
The distance travelled between the moment you 1st see a hazard and the moment
when you use the break.
