Chapter Preview Questions 1.Is a moving bus a good reference point from which to measure your position? a. No, because it is often late. b. No, because.

Chapter Preview Questions

1. Is a moving bus a good reference point from which to measure your position?

a. No, because it is often late.

b. No, because it is not a stationary object.

c. Yes, because it is very large.

d. Yes, because it can travel very far.

Chapter 9 Motion and Energy


1. Is a moving bus a good reference point from which to measure your position?

a. No, because it is often late.

b. No, because it is not a stationary object.

c. Yes, because it is very large.

d. Yes, because it can travel very far.



2. To describe a friend’s position with respect to you, you need to know

a. Your friend’s distance from you.

b. The direction your friend is facing.

c. Your friend’s distance and direction from you.

d. Your friend’s distance from a nearby object.



2. To describe a friend’s position with respect to you, you need to know

a. Your friend’s distance from you.

b. The direction your friend is facing.

c. Your friend’s distance and direction from you.

d. Your friend’s distance from a nearby object.



3. Two cars traveling in the same direction pass you at exactly the same time. The car that is going faster

a. moves farther in the same amount of time.

b. has more mass.

c. has the louder engine.

d. has less momentum.



3. Two cars traveling in the same direction pass you at exactly the same time. The car that is going faster

a. moves farther in the same amount of time.

b. has more mass.

c. has the louder engine.

d. has less momentum.



4. To describe an object’s motion, you need to know its

a. position.

b. change in position.

c. distance.

d. change in position over time.



4. To describe an object’s motion, you need to know its

a. position.

b. change in position.

c. distance.

d. change in position over time.


You are in a stationary car and another car passes you. How would you describe the motion of the other car?

How can you describe an object’s motion?


Section 1: Describing Motion

Standard 8.1.a Students know position is defined in relation to some choice of a standard reference point and a set of reference directions.


Section 1: Describing MotionWhen is an object in motion?

reference point

An object is in motion if it changes position relative to a reference point.

A place or object used for comparison to determine if something is in motion.


Relative MotionWhether or not an object is in motion depends on the reference point you choose.

Chapter 9 Motion and Energy - Describing Motion

Section 1: Describing MotionWhat is the difference between distance and displacement?

vector

Distance is the total length of the actual path between two points. Displacement is the length and direction of a straight line between starting and ending points.

A quantity that consists of both a magnitude and a direction.


Distance and Displacement


Section 1 Quick QuizWhen an object’s distance from another object is changing,

A.it has a high velocity.

B.it is accelerating.

C.it is in motion.

D.it is moving at a constant speed.

Answer – C – it is in motion

Section 1 Quick QuizA place or object used for comparison to determine if something is in motion is called

A.velocity.

B.a reference point.

C.a position.

D.a constant.

Answer – B – a reference point

Section 2: Speed and Velocity

Standard 8.1.b Students know that average speed is the total distance traveled divided by the total time elapsed and that the speed of an object along the path traveled can vary.

Standard 8.1.c Students know how to solve problems involving distance, time, and average speed.

Standard 8.1.d Students know the velocity of an object must be described by specifying both the direction and the speed of the object.


Calculating SpeedHow do you calculate speed?

speed

To calculate the speed of an object, divide the distance an object travels by the amount of time it takes to travel that distance.

The distance an object travels per unit of time.

Speed = Distance

Time


Calculating SpeedIf a distance runner runs 10 miles in one hour, what is her speed?

Instantaneous speed

The runner’s speed is 10 miles per hour.

Speed = 10 miles

1 hour

The rate at which an object is moving at a given instant in time.


Calculating SpeedHow do you calculate average speed?

A cyclist travels 32 kilometers during the first 2 hours. Then he travels 13 kilometers during the next hour. What is his average speed?

To calculate average speed (v), divide the total distance traveled (d) by the total time (t).

Average Speed = Total Distance

(v) Total Time

v = 32 km + 13 km = 45 km

2 h + 1 h = 3 h

v = 15 km/h


VelocityHow can you describe changes in velocity?

Changes in velocity may be due to changes in speed, changes in direction, or both.•Like displacement, velocity is a vector.•It has magnitude and direction.

A jet airplane’s velocity could be described as 700 miles per hour to the east.


Graphing SpeedHow can you interpret graphs of distance versus time?

The slope of a distance-versus-time graph represents speed, that is, the rate that distance changes in relation to time.•Time is shown on the horizontal axis, or x-axis.•Distance, or position, is shown on the vertical axis, or y-axis.•A point on the line represents the distance an object has traveled from the origin or a reference point at a particular time.


Graphing Motion

You can use distance-versus-time graphs to interpret motion.


Section 2 Quick QuizSpeed equals distance divided by

A.size.

B.time.

C.velocity.

D.motion.

Answer – B - time

Section 2 Quick QuizWhen you know both the speed and direction of an object’s motion, you know the

A.velocity of the object.

B.distance the object has traveled.

C.acceleration of the object.

D.average speed of the object.

Answer – A – velocity of the object

Section 2 Quick QuizAverage speed is

A.equivalent to velocity.

B.the total distance traveled divided by the total time.

C.the rate at which an object is moving at a given instant.

D.the rate at which a slope changes.

Answer – B – the total distance traveled divided by the total time

Section 2 Quick QuizIf the speed of an object does NOT change, the object is traveling at a

A.increasing speed.

B.decreasing speed.

C.constant speed.

D.average speed.

Answer – C – constant speed

Section 2 Quick QuizIf a bicyclist travels 32 miles in 4 hours, her average speed is

A.8 mi/h.

B.4 mi/h.

C.16 mi/h.

D. 128 mi/h.

Answer – A – 8 mi/h

Section 2 Quick QuizIf an object moves in the same direction and at a constant speed for 8 hours, which of the following is true?

A.The object accelerated during the 8 hours.

B.The object decelerated during the 8 hours.

C.The object’s speed changed during the 8 hours.

D.The object’s velocity did not change.

Answer – D – The object’s velocity did not change.

Section 2 Quick QuizIf you know a car traveled 250 miles in 5 hours, you can find its

A.direction.

B.average speed.

C.velocity.

D.acceleration.

Answer – B – average speed

Section 2 Quick QuizA car travels 100 km in the first hour of a trip. The car continues to travel for 4 more hours and travels 350 km. What was the average speed of the car for the trip:

A.95 km/h.

B.88 km/h.

C.90 km/h.

D.111 km/h.

Answer – C – 90 km/h

Section 2 Quick QuizIn a graph of distance versus time, the slope represents

A.speed.

B.acceleration.

C.potential energy.

D.displacement.

Answer – A - speed

Section 2 Quick QuizThe rise of a line on a distance-versus-time graph is 600 km and the run is 30 hours. What is the speed of the object represented by this graph?

A.200 km/h

B.450 km/h

C.20 km/h

D.1800 km/h

Answer – C – 20 km/h

Section 3: Acceleration

Standard 8.1.e Students know changes in velocity may be due to changes in speed, direction, or both.

Standard 8.1.f Students know how to interpret graphs of position versus time and graphs of speed versus time for motion in a single direction.


Changing VelocityWhat kind of motion does acceleration refer to?

In science, acceleration refers to increasing speed, decreasing speed, or changing direction.

Just as objects can speed up, they can also slow down. This change in speed is sometimes called deceleration, or negative acceleration.

An object that is traveling at a constant speed can be accelerating if it is changing direction.


Changing VelocityHow do you calculate acceleration?

Acceleration =

To determine the acceleration of an object, you must calculate its change in velocity per unit of time.

Final Velocity – Initial Velocity

Time


Calculating AccelerationTo determine the acceleration of an object, you must calculate its change in velocity per unit of time.


Calculating AccelerationAs a roller-coaster car starts down a slope, its velocity is 4 m/s. But 3 seconds later, its velocity is 22 m/s in the same direction. What is its acceleration?

Read and Understand

What information have you been given?

Initial velocity = 4 m/s

Final velocity = 22 m/s

Time = 3 s


Calculating AccelerationAs a roller-coaster car starts down a slope, its velocity is 4 m/s. But 3 seconds later, its velocity is 22 m/s in the same direction. What is its acceleration?Plan and SolveWhat quantity are you trying to calculate?

The acceleration of the roller-coaster car = __What formula contains the given quantities and the unknown quantity?

Acceleration = (Final velocity - Initial velocity)/TimePerform the calculation.

Acceleration = (22 m/s - 4 m/s)/3 s = 18 m/s/3 sAcceleration = 6 m/s2

The acceleration is 6 m/s2 down the slope .


Calculating AccelerationAs a roller-coaster car starts down a slope, its velocity is 4 m/s. But 3 seconds later, its velocity is 22 m/s in the same direction. What is its acceleration?

Look Back and Check

Does your answer make sense?

The answer is reasonable. If the car’s velocity increases by 6 m/s each second, its velocity will be 10 m/s after 1 second, 16 m/s after 2 seconds, and 22 m/s after 3 seconds.


Calculating Acceleration

Practice Problem

A falling raindrop accelerates from 10 m/s to 30 m/s in 2 seconds. What is the raindrop’s acceleration?

(30 m/s - 10 m/s) ÷ 2 seconds = 10 m/s2


Calculating Acceleration

Practice Problem

A certain car can accelerate from rest to 27 m/s in 9 seconds. Find the car’s acceleration.

(27 m/s - 0 m/s) ÷ 9 s = 27 m/s ÷ 9 s = 3 m/s2


Graphing Acceleration

You can use both a speed-versus-time graph and a distance-versus-time graph to analyze the motion of an accelerating object.


Section 3 Quick QuizWhich of these is an example of deceleration?

A.a car moving after a green light

B.a train coming in to its station

C.a roller coaster moving down a steep hill

D.an airplane following a straight flight path

Answer – B – a train coming in to its station

Section 3 Quick QuizThe moon accelerates because it is

A.in a vacuum in space.

B.a very large sphere.

C.continuously changing direction.

D.constantly increasing its speed and orbit.

Answer – C – continuously changing direction

Section 3 Quick QuizIf speed is measured in kilometers per hour and time is measured in hours, the unit of acceleration is

A.kilometers.

B.kilometers per hour per hour.

C.kilometers per hour.

D.hours.

Answer – B – kilometers per hour per hour

Section 3 Quick QuizWhich of the following is the correct equation for acceleration?

A.acceleration = (final speed – initial speed)/time

B.acceleration = (final speed – initial speed) x time

C.acceleration = time/(final speed – initial speed)

D.acceleration = (initial speed – final speed)/time

Answer – A - acceleration = (final speed – initial speed)/time

Section 3 Quick QuizIn a graph showing speed versus time, a straight line shows the acceleration is

A.decreasing.

B.increasing.

C.changing.

D.constant.

Answer – D - constant

Section 4: Energy

Standard 8 Framework Students should begin to grasp four concepts that help to unify physical sciences: force and energy; the laws of conservation;…


Kinetic EnergyWhat factors affect an object’s kinetic energy and potential energy?

Kinetic Energy =

The kinetic energy of an object depends on both its mass and its speed.

Kinetic energy increases as mass increases.

Kinetic energy also increases when speed increases.

½ x Mass x Speed2


Kinetic Energy

Kinetic energy increases as mass and speed increase.


Exponents An exponent tells how many times a number is used as a factor. For example, 3 x 3 can be written as 32. You read this number as “three squared.” In the formula for kinetic energy, speed is squared. For example, you can calculate the kinetic energy of a 70-kg person moving at a speed of 2 m/s by using the formula below.

KE = ½ x Mass x Speed2

= ½ x 70 kg x (2 m/s) 2

= 140 kg•m2/s2 or 140 joules.

Note:

1 kg•m2/s2 = 1 joule


Exponents Practice Problem

What is the kinetic energy of a 30-kg rock moving at a speed of 10 m/s?

1,500 joules


Potential Energypotential energy Stored energy that results from

the position or shape of an object.


Potential Energy

Gravitational potential energy increases as weight and height increase.


Transformations BetweenPotential and Kinetic Energy

A pendulum continuously transforms energy from kinetic to potential energy and back.


Section 4 Quick QuizThe energy associated with motion is called

A.elastic potential energy.

B.gravitational potential energy.

C.nuclear energy.

D.kinetic energy.

Answer – D – kinetic energy

Section 4 Quick QuizWhich of the following has kinetic energy?

A.a rock poised for a fall

B.an archer’s bow that is drawn back

C.a boat going downstream

D.a car waiting at a red light

Answer – C – a boat going downstream

Section 4 Quick QuizPotential energy that depends on height is called

A.mechanical energy.

B.elastic potential energy.

C.kinetic energy.

D.gravitational potential energy.

Answer – D – gravitational potential energy

Chapter Preview Questions 1.Is a moving bus a good reference point from which to measure your position? a. No, because it is often late. b. No, because.

Documents

motion slide

objects motion

motion standard

relative motion

energy slide

chapter preview questions

friends position

friends distance