Physics Chapter 3: Accelerated Motion

What is acceleration?

The rate at which an object’s velocity changes. (The rate of change of velocity.)

What is uniform motion?

Motion with constant velocity— the object moves at the same speed in the same direction.

What is nonuniform motion?

Motion where velocity changes— the object speeds up, slows down, or changes direction.

Is acceleration a scalar or vector quantity?

Vector— it has both magnitude and direction.

What does the + or - sign of acceleration tell you?

It tells you the direction of acceleration. It does NOT automatically tell you whether an object is speeding up or slowing down.

What is Kinematics?

The study of motion without considering the forces causing the motion.

Can an object accelerate while traveling at constant speed?

Yes— if its direction changes, its velocity changes, so it is accelerating. EX: a car going around a curve at constant speed.

What is average acceleration?

The change in velocity divided by the time interval: A= Vf-Vi/Tf-Ti

What does an object speed up?

When velocity and acceleration point in the SAME direction.

When does an object slow down?

When velocity and acceleration point in OPPOSITE directions.

A car has +v and +a. It is speeding up or slowing down?

Speeding up— both vectors point in the same direction.

A car has +v and -a. Is it speeding up or slowing down?

Slowing down— vectors point in OPPOSITE directions.

A car has -v and -a. Is it speeding up or slowing down?

Speeding up— both vectors point in the same direction.

On a motion diagram, what does increasing spacing between dots indicate?

The object is speeding up.

On a motion diagram, what does decreasing spacing between dots indicate?

The object is slowing down.

On a motion diagram, what does the length of the velocity arrow represent?

The magnitude(speed) of the velocity.

What does the slope of a velocity-time graph represent?

Accleration. Slope= Vf-Vi/Tf-Ti

What does a horizontal line on a velocity-time graph indicate?

Constant velocity and zero acceleration.

What does a straight sloped line on a velocity-time graph indicate?

Constant Acceleration.

On a velocity-time graph, how can you tell the object is moving in the negative direction?

The velocity values are below the x-axis(negative).

On a velocity-time graph, how can you tell the object has zero acceleration?

The graph is horizontal(flat line)— velocity is not changing.

On a velocity-time graph, how can you tell the object is slowing down while moving in the positive direction?

Velocity is positive but decreasing toward 0(line has negative slope, about x-axis.)

On a velocity-time graph, if the line has negative slope and the velocity is negative, is the object slowing down?

No— it is speeding us in the negative direction(both velocity and acceleration are negative=same direction).

What are the axes of a velocity-time graph?

x-axis= time (independent variable); y-axis= velocity (dependent variable)

What does the slope of a position-time graph represent?

Velocity

Whatn shape is a position-time graph for constant acceleration?

A curve (parabola/quadratic relationship)— because velocity is changing, so the slope is changing.

Why is a position-time graph curved for constant acceleration?

Because velocity(the slope) is changing over time— equal time intervals do NOT produce changes in position.

What does a straight line on a position-time graph indicate?

Constant velocity(zero acceleration).

What is the formula for average acceleration?

A= Vf-Vi/Tf-Ti

A car increases velocity from 4.0 m/s to 16.0 m/s in 6.0s. What is the average velocity?

+2 m/s² (velocity increases 2 m/s every second)

A cyclist slows from 18 m/s to 6.0 m/s in 4.0s. What is the average acceleration?

-3m/s² (negative= slowing down)

What does “start from rest” mean in Kinematics?

V_i=0

What does “comes to a stop” mean in Kinematics?

V_f= 0

What does “returns to its starting position” mean in Kinematics?

X(displacement)= 0

What does “constant velocity” mean in kinematics?

A =0

What does “speeds up” tell you about the directions of v and a?

velocity and acceleration have the same direction

What does “slows down” tell you about the directions of v and a?

Velocity and acceleration have opposite directions.

What does the area between a velocity-time grapg and the time axis represent?

Displacement

How do you find displacement from a velocity-time graph when the shape is a triangle?

Area= ½ x base x height = ½ x t x v

How do you find displacement from a velocity-time graph when the shape is a rectangle?

Area= length x width = t x v

If the area under a velocity-time graph is below the x-axis (negative velocity region), what does that mean for displacement?

The displacement is negative— the object moved in the negative direction during that interval.