(numerical value)

Displacement problems will find the

distance from the starting point to the

ending point.

In calculating, you will find the total distance traveled.

*Calculate the total amount traveled

What formula for triangles?

*Here we have to consider the direction…

Bellringer-9/4/14

1. What is the difference between

distance and displacement?

2. Solve for distance and

displacement:

A

7

B 8 C

Motion & Forces

Describing Motion Motion

Speed & Velocity

Acceleration

Newton’s First Law

Newton’s First Law of Motion

An object at rest will remain at

rest and an object in motion

will continue moving at a

constant velocity unless acted

upon by a net force.

motion

constant velocity

net force

A. Motion

Problem:

Is your desk moving?

We need a reference point...

nonmoving point from which

motion is measured

A. Motion

Motion

Change in position in relation to

a reference point.

Reference point

Motion

A. Motion

Problem:

You are a passenger in a car

stopped at a stop sign. Out of the

corner of your eye, you notice a

tree on the side of the road begin

to move forward.

You have mistakenly set yourself

as the reference point.

B. Speed & Velocity

Speed

rate of motion

Speed is the distance traveled per

unit time

If you know the distance an object

traveled in a set time, you can

calculate speed

time

distancespeed

vd

t

B. Speed & Velocity

Instantaneous Speed

speed at a given instant

Average Speed

time total

distance totalspeed avg.

B. Speed & Velocity

Problem:

A storm is 10 km away and is

moving at a speed of 60 km/h.

Should you be worried?

It depends

on the

storm’s

direction!

B. Speed & Velocity

Velocity

speed in a given direction (it is

a vector!)

can change even when the

speed is constant! (storms!)

Speed v. Velocity

1. How are speed and velocity similar?They both measure how fast something is

moving

2. How are speed and velocity different?Velocity includes the direction of motion and

speed does not (the car is moving 5mph East)

3. Is velocity more like distance or displacement? Why?

Displacement, because both are vectors which include an amount and a direction.

C. Acceleration

Acceleration

rate at which velocity changes

change in speed or direction

t

vva

if

a: acceleration

vf: final velocity

vi: initial velocity

t: time

a

vf - vi

t

C. Acceleration

Positive acceleration

“speeding up”

Negative acceleration

“slowing down”

D. Calculations

Your neighbor skates at a speed of 4 m/s.

You can skate 100 m in 20 s. Who skates

faster?

GIVEN:

d = 100 m

t = 20 s

v = ?

WORK:

v = d ÷ t

v = (100 m) ÷ (20 s)

v = 5 m/s

You skate faster!v

d

t

D. Calculations

A roller coaster starts down a hill at 10 m/s.

Three seconds later, its speed is 32 m/s.

What is the roller coaster’s acceleration?

GIVEN:

vi = 10 m/s

t = 3 s

vf = 32 m/s

a = ?

WORK:

a = (vf - vi) ÷ t

a = (32m/s - 10m/s) ÷ (3s)

a = 22 m/s ÷ 3 s

a = 7.3 m/s2a

vf - vi

t

D. Calculations

Sound travels 330 m/s. If a lightning bolt

strikes the ground 1 km away from you,

how long will it take for you to hear it?

GIVEN:

v = 330 m/s

d = 1km = 1000m

t = ?

WORK:

t = d ÷ v

t = (1000 m) ÷ (330 m/s)

t = 3.03 s

v

d

t

D. Calculations

How long will it take a car traveling 30 m/s

to come to a stop if its acceleration is

-3 m/s2?

GIVEN:

t = ?

vi = 30 m/s

vf = 0 m/s

a = -3 m/s2

WORK:

t = (vf - vi) ÷ a

t = (0m/s-30m/s)÷(-3m/s2)

t = -30 m/s ÷ -3m/s2

t = 10 sa

vf - vi

t

E. Graphing Motion

slope =

steeper slope =

straight line =

flat line =

Distance-Time Graph

A

B

faster speed

constant speed

no motion

speed

E. Graphing Motion

Who started out faster?

A (steeper slope)

Who had a constant speed?

A

Describe B from 10-20 min.

B stopped moving

Find their average speeds.

A = (2400m) ÷ (30min)

A = 80 m/min

B = (1200m) ÷ (30min)

B = 40 m/min

Distance-Time Graph

A

B

0

100

200

300

400

0 5 10 15 20

Time (s)

Dis

tan

ce

(m

)

Distance-Time Graph

E. Graphing Motion

Acceleration is

indicated by a

curve on a

Distance-Time

graph.

Changing slope =

changing velocity

E. Graphing Motion

0

1

2

3

0 2 4 6 8 10

Time (s)

Sp

ee

d (

m/s

)

Speed-Time Graph

slope =

straight line =

flat line =

acceleration

+ve = speeds up

-ve = slows down

constant accel.

no accel.

(constant velocity)

E. Graphing Motion

0

1

2

3

0 2 4 6 8 10

Time (s)

Sp

ee

d (

m/s

)

Speed-Time Graph

Specify the time period

when the object was...

slowing down

5 to 10 seconds

speeding up

0 to 3 seconds

moving at a constant

speed

3 to 5 seconds

not moving

0 & 10 seconds

Newton’s Second LawGravity

Air Resistance Calculations

Newton’s Second Law of Motion

The acceleration of an object is

directly proportional to the net force

acting on it and inversely

proportional to its mass.

F = ma

F = ma

F: force (N)

m: mass (kg)

a: accel (m/s2)

1 N = 1 kg ·m/s2

am

F

a

F

m

Gravity

force of attraction between any

two objects in the universe

increases as...

mass increases

distance decreases

Who experiences more gravity - the

astronaut or the politician?

less

distance

more

mass

Which exerts more gravity -

the Earth or the moon?

Weight

the force of gravity on an object

MASSalways the same

(kg)

WEIGHTdepends on gravity

(N)

W = mgW: weight (N)

m: mass (kg)

g: acceleration due

to gravity (m/s2)

VS

Would you weigh more on Earth

or Jupiter?

greater gravity

greater weight

greater mass

Jupiter because...

Accel. due to gravity (g)

In the absence of air

resistance, all falling objects

have the same acceleration!

On Earth: g = 9.8 m/s2

mW

g

elephant

m

Fa

featherAnimation from “Multimedia Physics Studios.”

Air Resistance

a.k.a. “fluid friction” or “drag”

force that air exerts on a moving

object to oppose its motion

depends on:

• speed

• surface area

• shape

• density of fluid

Terminal Velocity

maximum velocity reached

by a falling object

reached when…

Fgrav = Fair

Fair

Fgrav

no net force

no acceleration

constant velocity

Terminal Velocity

increasing speed increasing

air resistance until…

Fair = FgravAnimation from “Multimedia Physics Studios.”

Falling with air resistance

Fgrav = Fair

Animation from “Multimedia Physics Studios.”

heavier objects fall faster

because they accelerate to

higher speeds before

reaching terminal velocity

larger Fgrav

need larger Fair

need higher speed

What force would be required to

accelerate a 40 kg mass by 4 m/s2?

GIVEN:

F = ?

m = 40 kg

a = 4 m/s2

WORK:

F = ma

F = (40 kg)(4 m/s2)

F = 160 N

m

F

a

A 4.0 kg shotput is thrown with 30 N of

force. What is its acceleration?

GIVEN:

m = 4.0 kg

F = 30 N

a = ?

WORK:

a = F ÷ m

a = (30 N) ÷ (4.0 kg)

a = 7.5 m/s2

m

F

a

Ms. F. weighs 557 N. What is her

mass?

GIVEN:

F(W) = 557 N

m = ?

a(g) = 9.8 m/s2

WORK:

m = F ÷ a

m = (557 N) ÷ (9.8 m/s2)

m = 56.8 kg

m

F

a

Is the following statement true or false?

An astronaut has less mass on the moon

since the moon exerts a weaker

gravitational force.

False! Mass does not depend on

gravity, weight does. The astronaut has

less weight on the moon.

Do Now

How would you describe how fast an object is moving?

Speed, Velocity, and Acceleration

Goals:

• To investigate what is needed to describe motion completely.

• To compare and contrast speed and velocity.

• To learn about acceleration.

To describe motion accurately and completely, a frame of reference is needed.

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

• Objects that we call stationary—such as a tree, a sign, or a building—make good reference points.

The passenger can use a tree as a reference point to decide if the train is moving. A tree makes a good reference point because it is stationary from the passenger’s point of view.

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

Distance

When an object moves, it goes from point A to point B – that is the DISTANCE it traveled. (SI unit is the meter)

AB

DisplacementKnowing how far something moves is not sufficient. You

must also know in what direction the object moved.

A quantity that has magnitudeand directionis called a…

VECTOR

SpeedCalculating Speed: If you know the distance an

object travels in a certain amount of time, you can calculate the speed of the object.

Speed = Distance/time Average speed = Total distance/Total time

What is instantaneous speed?

Velocity

Velocity is a description of an object’s speed and direction. It is a vector.

As the sailboat’s direction changes, its velocity also changes, even if its speed stays the same. If the sailboat slows down at the same time that it changes direction, how will its velocity be changed?

Speed v. Velocity

1. How are speed and velocity similar?They both measure how fast something is moving

2. How are speed and velocity different?Velocity includes the direction of motion and

speed does not (the car is moving 5mph East)

3. Is velocity more like distance or displacement? Why?

Displacement, because both are vectors which include an amount and a direction.

Graphing Speed

D

I

S

T

A

N

C

E

T I M E

Speed increasing

Object is stopped

Object begins moving at a different speed

The steepness of a line on a graph is called slope.

• The steeper the slope is, the greater the speed.

• A constant slope represents motion at constant speed.

Using the points shown, the rise is 400 meters and the run is 2 minutes. To find the slope, you divide 400 meters by 2 minutes. The slope is 200 meters per minute.

Do Now:

Set up formula triangles to find speed and velocity

Acceleration

Acceleration is the rate at which velocity changes.

Acceleration can result from a change in speed (increase or decrease), a change in direction (back, forth, up, down left, right), or changes in both. Like velocity, acceleration is a vector.

• The pitcher throws. The ball speeds toward the batter. Off the bat it goes. It’s going, going, gone! A home run!

• Before landing, the ball went through several changes in motion. It sped up in the pitcher’s hand, and lost speed as it traveled toward the batter. The ball stopped when it hit the bat, changed direction, sped up again, and eventually slowed down. Most examples of motion involve similar changes. In fact, rarely does any object’s motion stay the same for very long.

1. As the ball falls from the girl’s hand, how does its speed change?

Understanding Acceleration

2. What happens to the speed of the ball as it rises from the ground back to her hand?

3. At what point does the ball have zero velocity?

4. How does the velocity of the ball change when it bounces on the floor?

You can feel acceleration!

If you’re moving at 500mph east without turbulence, there is no acceleration.

But if the plane hits an air pocket and drops 500 feet in 2 seconds, there is a large change in acceleration and you will feel that!

It does not matter whether you speed up or slow down; it is still considered a change in

acceleration.

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

• A car that begins to move from a stopped position or speeds up to pass another car is accelerating.

• A car decelerates when it stops at a red light. A water skier decelerates when the boat stops pulling.

• A softball accelerates when it changes direction as it is hit.

Calculating Acceleration

Acceleration = Change in velocity

Total time

Change in velocity = final velocity-initial velocity

OR..

= final speed-initial speed

So…Acceleration = (Final speed – Initial speed)

Time

As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the

bottom, its speed is 22 m/s. What is its average acceleration?

Calculating Acceleration

What information have you been given?

Initial speed = 4 m/sFinal Speed = 22 m/sTime = 3 s

What quantity are you trying to calculate?

The average acceleration of the roller-coaster car.

What formula contains the given quantities and the

unknown quantity?

Acceleration = (Final speed – Initial speed)/Time

Perform the calculation.

Acceleration = (22 m/s – 4 m/s)/3 s = 18 m/s/3 s

Acceleration = 6 m/s2

The roller-coaster car’s average acceleration is 6 m/s2.

Calculating Acceleration

Graphing acceleration

S

P

E

E

D

T i m e

Object accele-rates

Object moves at constant speed

Object decelerates

The slanted, straight line on this speed-versus-time graph tells you that the cyclist is accelerating at a constant rate. The slope of a speed-

versus-time graph tells you the object’s acceleration. Predicting How would the slope of the graph change if the cyclist were accelerating at a

greater rate? At a lesser rate?

Since the slope is increasing, you can conclude that the speed is also increasing. You are accelerating.

Distance-Versus-Time Graph The curved line on this distance-versus-time graph tells you that the cyclist is accelerating.

Projectile Motion

Circular Motion

Free-fall

Projectileany object thrown in the air

acted upon only by gravity

follows a

parabolic path

called a trajectory

has horizontal and vertical velocitiesPROJECTILE MINI-LAB

Projectile Velocities

Horizontal and vertical velocities are

independent of each other!

Horizontal Velocity

depends on inertia

remains constant

Vertical Velocity

depends on gravity

accelerates downward at 9.8 m/s2

A moving truck launches a ball vertically (relative to the truck). If the truck maintains a constant horizontal velocity after the launch, where will the ball land (ignore air resistance)?

A) In front of the truck

B) Behind the truck

C) In the truck

C) In the truck. The

horizontal velocity of the

ball remains constant

and is unaffected by its

vertical motion. Animation from “Multimedia Physics Studios.”

Centripetal Acceleration

acceleration toward the center of a

circular path

caused by centripetal force

B-BALL DEMO

PLATE DEMO

On the ground... friction provides centripetal force

(Centripetal force is a force that makes a body follow a curved path)

In orbit...

gravity provides centripetal force

ROUND LAB

In orbit...

Which satellites travel faster?

Near-Earth Satellites Geostationary Satellites

Free-Fall

when an object is influenced only by

the force of gravity

Has a constant acceleration

Weightlessness

sensation produced when an object

and its surroundings are in free-fall

(no force of support on your body)

object is not weightless!

CUP DEMO

Weightlessness

surroundings are falling at the same

rate so they don’t exert a force on

the object

Go

to N

AS

A.

Go t

o C

NN

.com

.

Go t

o S

pac

e S

ettl

emen

t V

ideo

Lib

rary

.Space Shuttle Missions

TRUE or FALSE:

An astronaut on the Space Shuttle

feels weightless because there is no

gravity in space.

FALSE!

There is gravity which is causing the

Shuttle to free-fall towards the Earth.

She feels weightless because she’s

free-falling at the same rate.

Describe the path of a marble as it

leaves the spiral tube shown below.

It will travel in a straight line since the

tube is no longer exerting a net force

on it.

Solve:

1. If Ms. Farris walks 3 blocks east, 5 blocks south,

and 3 blocks west, what distance has she

traveled?

2. If Ms. Farris walks 3 blocks east, 5 blocks south,

and 3 blocks west, what is her displacement?

3. What is the momentum of a 3 kg toy truck that

moves at 30 m/s? (2 points)

How do we cite articles in APA format?

http://www.nbcnews.com/science/space/surpris

e-giant-black-hole-discovered-dwarf-galaxy-

n205896

http://www.sciencedaily.com/releases/2014/09/

140917131824.htm

https://owl.english.purdue.edu/owl/resource/56

0/01/

1 paragraph should be a summary of your

article; second paragraph should be your

reaction (5-7 sentences)

An object at rest will remain at rest and an object

in motion will continue moving at a constant

velocity unless acted upon by a net force.

The acceleration of an object is directly

proportional to the net force acting on it and

inversely proportional to its mass.

F=MA

What do those variables stand for?

When one object exerts force on a second object,

the second one exerts a force on the first that is

equal in strength and opposite in direction

Define the following on a sheet of paper in your own words

InertiaForceVelocitySpeedTerminal VelocityMassWeight

Force-The push or pull exerted on an object

Inertia-tendency of an object to resist motion

Speed-Rate of motion; Rate of change in an objects position

Velocity-Speed of object + it’s direction

Terminal Velocity-Largest velocity reached by falling object; point where gravity equals force

Mass-amount of matter in an object; does not change

Weight-changes based on gravity