Section 1 Measuring Motion

Explain the relationship between motion and a frame of reference.

Relate speed to distance and time.

Distinguish between speed and velocity.

Solve problems related to time, distance, displacement, speed, and velocity.

Chapter 10

Motion is an object’s change in position relative to a reference point.

Displacement is the change in the position of an object.

• Distance measures the path taken.• Displacement is the change of an object’s

position. Displacement must always indicate direction.

Section 1 Measuring MotionChapter 10

Section 1 Measuring MotionChapter 10

Section 1 Measuring MotionChapter 10

Speed is the distance traveled divided by the time interval during which the motion occurred. Speed describes how fast an object moves.

Speed measurements involve distance and time.

• The SI units for speed are meters per second (m/s).• When an object covers equal distances in equal

amounts of time, it is moving at a constant speed.

Section 1 Measuring MotionChapter 10

Section 1 Measuring MotionChapter 10

Speed can be studied with graphs and equations.

Speed can be determined from a distance-time graph. When an object’s motion is graphed by plotting distance on the y-axis and time on the x-axis, the slope of the graph is speed.

Section 1 Measuring MotionChapter 10

Average speed is calculated as distance divided by time.Equation for Average Speed

speed = distance

time v = dt

Section 1 Measuring MotionChapter 10

• Instantaneous speed is the speed at a given point in time.

Velocity Metal stakes are sometimes placed in glaciers to help measure a glacier’s movement. For several days in 1936, Alaska’s Black Rapids glacier surged as swiftly as 89 meters per day down the valley. Find the glacier’s velocity in m/s. Remember to include direction.

1. List the given and the unknown values.Given:m down the valleyUnknown:

Section 1 Measuring MotionChapter 10

2. Perform any necessary conversions.To find the velocity in meters per second, the value for time must be in seconds.

Section 1 Measuring MotionChapter 10

speed = displacement

time = dt

3. Write the equation for speed.

v = dt =

89 m8.64 104 s

(For velocity, include direction.)

v = 1.0 10–3 m/s down the valley

Section 1 Measuring MotionChapter 10

4. Insert the known values into the equation, and solve.

Velocity is the speed of an object in a particular direction.

Velocity describes both the speed and the direction.

Combine velocities to determine the resultant velocity.

Section 1 Measuring MotionChapter 10

Section 1 Measuring MotionChapter 10

Section 1 Measuring MotionChapter 10

Visual Concept

Section 2 Acceleration

Describe the concept of acceleration as a change in velocity.

Explain why circular motion is continuous acceleration even when the speed does not change.

Calculate acceleration as the rate at which velocity changes.

Graph acceleration on a velocity-time graph.

Chapter 10

Acceleration is the rate at which velocity changes over time.

An object accelerates if its speed, direction, or both change.

Section 2 AccelerationChapter 10

Section 2 AccelerationChapter 10

Acceleration can be a change in speed.

Acceleration can be a change in direction.

Uniform circular motion is constant acceleration.

Section 2 AccelerationChapter 10

Section 2 AccelerationChapter 10

Acceleration is the rate at which velocity changes.Acceleration Equation (for straight-line motion)

acceleration = final velocity – initial velocity

time a = ∆vt

Section 2 AccelerationChapter 10

• In SI units, acceleration is measured in meters per second per second (m/s/s) or m/s2.

Acceleration A flowerpot falls off a second-story windowsill. The flowerpot starts from rest and hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. Find the average acceleration of the flowerpot.

1. List the given and the unknown values.Given:

Unknown:

Section 2 AccelerationChapter 10

3. Insert the known values into the equation, and solve.

Section 2 AccelerationChapter 10

2. Write the equation for acceleration.

Acceleration can be determined from a velocity-time graph.

Section 2 AccelerationChapter 10

Section 2 AccelerationChapter 10

Section 3 Motion and Force

Explain the effects of unbalanced forces on the motion of objects.

Compare and contrast static and kinetic friction.

Describe how friction may be either harmful or helpful.

Identify ways in which friction can be reduced or increased.

Chapter 10

Force is an action exerted on a body in order to change the body’s state of rest or motion. Force has magnitude and direction.• The net force is the combination of all forces

acting on an object.

Objects subjected to balanced forces either do not move or move at constant velocity.

An unbalanced force must be present to cause any change in an object’s state of motion or rest.

Section 3 Motion and ForceChapter 10

Section 3 Motion and ForceChapter 10

Friction is a force that opposes motion between two surfaces that are in contact.

Friction opposes the applied force.

Section 3 Motion and ForceChapter 10

Section 3 Motion and ForceChapter 10

Static friction resists the initiation of sliding motion between two surfaces that are in contact and at rest.

Kinetic friction opposes the movement of two surfaces that are in contact and are sliding over each other.

Static friction is greater than kinetic friction. • There are many different types of kinetic friction,

such as sliding friction and rolling friction. • Fluid friction, such as air resistance, also opposes

motion.

Section 3 Motion and ForceChapter 10

Section 3 Motion and ForceChapter 10

Section 3 Motion and ForceChapter 10

Friction can be helpful or harmful.• Friction is necessary to roll a vehicle or hold an

object.• However, friction can also cause excessive

heating or wear of moving parts.

Harmful friction can be reduced.

Helpful friction can be increased.

Section 3 Motion and ForceChapter 10

Section 3 Motion and ForceChapter 10