Glossary
Acceleration
The rate at which an object's velocity changes over time. It is a vector quantity, meaning it has both magnitude and direction.
Example:
When a car speeds up from a stoplight, it experiences positive acceleration.
Acceleration (from P-T graph)
Indicated by a curved line on a position vs. time graph. A changing slope signifies that the object's velocity is changing.
Example:
When a roller coaster speeds up down a hill, its acceleration would be visible as a curve on its position-time graph, getting steeper over time.
Acceleration (from V-T graph)
The slope of a velocity vs. time graph represents the acceleration of the object. A positive slope means speeding up in the positive direction, while a negative slope means slowing down in the positive direction or speeding up in the negative direction.
Example:
If a velocity-time graph shows a line going from 0 m/s to 10 m/s in 2 seconds, the acceleration is 5 m/s², which is the slope.
Acceleration vs. Time Graphs
Graphs that plot an object's acceleration on the y-axis against time on the x-axis. The area under the curve represents the change in velocity.
Example:
An acceleration vs. time graph for a car braking steadily would show a constant negative value.
Average Acceleration
The total change in velocity divided by the total time interval over which the change occurred. It describes the overall rate of velocity change.
Example:
If a sprinter goes from 0 m/s to 10 m/s in 2 seconds, their average acceleration is 5 m/s².
Changing acceleration (from V-T graph)
Indicated by a curved line on a velocity vs. time graph. This means the object's acceleration itself is changing over time.
Example:
If a car's engine sputters and then catches, its velocity-time graph might show a changing acceleration as the curve's slope varies.
Constant acceleration (from A-T graph)
Indicated by a horizontal line (zero slope) on an acceleration vs. time graph. This means the object's acceleration is not changing.
Example:
An object in free fall has constant acceleration due to gravity, which would appear as a flat line at -9.8 m/s² on its acceleration-time graph.
Constant acceleration (from V-T graph)
Indicated by a straight, non-horizontal line on a velocity vs. time graph. This means the object's velocity is changing at a steady rate.
Example:
An object in free fall (ignoring air resistance) experiences constant acceleration due to gravity, which would appear as a straight, downward-sloping line on its velocity-time graph.
Constant velocity (from P-T graph)
Indicated by a straight line with a non-zero slope on a position vs. time graph. This means the object is moving at a steady speed in a single direction.
Example:
A car on cruise control on a straight highway would show constant velocity on its position-time graph, appearing as a perfectly straight, sloped line.
Constant velocity (from V-T graph)
Indicated by a horizontal line (zero slope) on a velocity vs. time graph. This means the object's velocity is not changing.
Example:
A train moving steadily at 100 km/h would show a flat, horizontal line on its velocity-time graph, representing constant velocity.
Displacement
The change in an object's position, measured as the straight-line distance and direction from the initial to the final position. It is a vector quantity.
Example:
If you walk 5 meters east and then 5 meters west, your total displacement is 0 meters, even though you walked 10 meters.
Displacement (from V-T graph)
The area under the curve of a velocity vs. time graph represents the displacement of the object. Area above the x-axis is positive displacement, below is negative.
Example:
To find how far a rocket traveled, you would calculate the displacement by finding the area under its velocity-time graph.
Distance
The total length of the path traveled by an object, regardless of direction. It is a scalar quantity.
Example:
If you walk 5 meters east and then 5 meters west, the total distance you traveled is 10 meters.
Frame of Reference
A coordinate system or point of view from which motion is observed and described. All motion is relative to a chosen frame of reference.
Example:
When you're on a moving train, a person walking down the aisle is moving relative to you, but also moving much faster relative to someone standing on the platform. This highlights the importance of the chosen frame of reference.
Inertial Reference Frame
A frame of reference where Newton's first law of motion holds true, meaning an object at rest stays at rest and an object in motion stays in motion with constant velocity unless acted upon by a net force.
Example:
A car moving at a constant speed in a straight line can be considered an inertial reference frame for objects inside it, as long as it doesn't accelerate or turn.
Initial acceleration (from A-T graph)
The y-intercept of an acceleration vs. time graph, representing the object's acceleration at time t=0.
Example:
If an acceleration-time graph starts at (0s, 3m/s²), then 3 m/s² is the initial acceleration of the object.
Initial displacement (from P-T graph)
The y-intercept of a position vs. time graph, representing the object's starting position at time t=0.
Example:
If a position-time graph starts at (0s, 5m), then 5 meters is the initial displacement of the object from the origin.
Initial velocity (from V-T graph)
The y-intercept of a velocity vs. time graph, representing the object's velocity at time t=0.
Example:
If a velocity-time graph starts at (0s, 15m/s), then 15 m/s is the initial velocity of the object.
Jerk (from A-T graph)
The slope of an acceleration vs. time graph represents the rate of change of acceleration, known as jerk. It's less commonly tested in AP Physics 1 but good to know.
Example:
If a car suddenly slams on its brakes, the rapid change in deceleration would result in a high jerk value on an acceleration-time graph.
Object at rest (from P-T graph)
Represented by a horizontal line (zero slope) on a position vs. time graph. This means the object's position is not changing over time.
Example:
If a soccer ball is sitting motionless on the field, its position-time graph would be a flat, horizontal line, indicating the object at rest.
Position
An object's location relative to a fixed origin or reference point. It is a vector quantity, though often represented by a single coordinate in one-dimensional motion.
Example:
If your house is at the origin (0 meters), then your friend's house 500 meters down the road has a position of +500 m.
Position vs. Time Graphs
Graphs that plot an object's position on the y-axis against time on the x-axis. Their slope indicates velocity, and their shape reveals acceleration.
Example:
Analyzing a position vs. time graph for a runner can show if they are speeding up, slowing down, or standing still at different points in their race.
Scalar
A physical quantity that has magnitude (size) only, without direction. Examples include distance, speed, mass, and temperature.
Example:
The temperature outside is 25 degrees Celsius; this is a scalar quantity because it only has a value, not a direction.
Speed
The rate at which an object covers distance. It is a scalar quantity, calculated as distance divided by time.
Example:
A car traveling at 60 miles per hour has a speed of 60 mph, regardless of its direction.
Vector
A physical quantity that has both magnitude (size) and direction. Examples include displacement, velocity, acceleration, and force.
Example:
To describe the wind, you need to say it's blowing at 15 km/h (magnitude) north (direction), making it a vector quantity.
Velocity
The rate at which an object changes its position, including both its speed and direction. It is a vector quantity, calculated as displacement divided by time.
Example:
A car traveling at 60 miles per hour north has a velocity of 60 mph north.
Velocity (from A-T graph)
The area under the curve of an acceleration vs. time graph represents the change in velocity of the object. This area can be positive or negative.
Example:
To find how much a rocket's speed increased, you would calculate the velocity change by finding the area under its acceleration-time graph.
Velocity (from P-T graph)
The slope of a position vs. time graph represents the velocity of the object. A steeper slope indicates a greater speed.
Example:
On a position-time graph, if the line goes from (0s, 0m) to (5s, 10m), the velocity is 2 m/s, which is the slope.
Velocity vs. Time Graphs
Graphs that plot an object's velocity on the y-axis against time on the x-axis. Their slope indicates acceleration, and the area under the curve represents displacement.
Example:
A velocity vs. time graph for a braking car would show a downward sloping line, indicating negative acceleration.