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Force and Motion Standards

- S8P3 Students will investigate the relationship

between force, mass, and the motion of objects. - a. Determine the relationship between velocity

and acceleration. - b. Demonstrate the effect of balanced and

unbalanced forces on an object in terms of

gravity, inertia, and friction.

- S8P3 Students will investigate the relationship

between force, mass, and the motion of objects. - a. Determine the relationship between velocity

and acceleration. Additional vocabulary

reference point, meter, speed, average speed,

instantaneous speed, slope, distance,

displacement - b. Demonstrate the effect of balanced and

unbalanced forces on an object in terms of

gravity, inertia, and friction. Additional

vocabulary newton, net force, mass, weight

Force and Motion Standards

- S8P5 Students will recognize characteristics of

gravity, electricity, and magnetism as major

kinds of forces acting in nature. - a. Recognize that every object exerts

gravitational force on every other object and

that the force exerted depends on how much mass

the objects have and how far apart they are.

What do we need to know and be able to do?

Essential Question

- How would you describe how fast an object is

moving? - Supporting Questions
- How is it possible to be accelerating and

traveling at a constant speed? - Why is it more important to know a tornados

velocity than its speed?

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 stationarysuch as a tree, a

sign, or a buildingmake 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 passengers point of view.

Describing Motion

Whether 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) - Distance is how much ground an object has covered

during its motion.

B

A

Displacement

- Knowing how far something moves is not

sufficient. You must also know in what direction

the object moved. -

Displacement is how - far our of place the
- object is it is the
- objects overall
- change in position.

Speed

- Calculating Speed If you know the distance an

object travels in a certain amount of time, you

can calculate the speed of the object.

What is instantaneous speed? Instantaneous

speed is the velocity of an object at a certain

time.

Speed Distance/time

Average speed Total distance/Total time

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Describing Motion

2.1

Velocity

Because velocity depends on direction as well as

speed, the velocity of an object can change even

if the speed of the object remains constant.

The speed of this car might be constant, but its

velocity is not constant because the direction of

motion is always changing.

Velocity

- Velocity is a description of an objects speed

and direction.

As the sailboats 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

- 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) - Is velocity more like distance or displacement?

Why? - Displacement, because it includes direction.

Graphing Speed

D I S T A N C E

Speed increasing

Object begins moving at a different speed

Object is stopped

T I M E

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.

Formula for Calculating SpeedSpeed Distance

time

Problem Solving Calculating Speed

What is the speed of a sailboat that is traveling

120 meters in 60 seconds? Step 1 Decide what

the problem is asking? A boat traveled 120 meters

in 60 seconds. What was the speed of the

boat? Step 2 What is the formula to calculate

speed? Speed Distance/Time Step 3 Solve

the problem using the formula Speed 120

meters 60 seconds 2 m/s So, the boat

was traveling at 2 m/s Now you try What is the

speed of a car that is traveling 150 miles in 3

hours?

Answer

- Step 1 What are the facts in the problem?
- A car is traveling 150 miles in 3 hours.
- Step 2 What is the formula to solve the

problem? Speed Distance/Time - Step 3 Solve the problem.
- Speed 150 miles 3 hours
- Speed 50 miles/hr.
- So, the car is traveling 50 miles/hr.

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.

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- The pitcher throws. The ball speeds toward the

batter. Off the bat it goes. Its going, going,

gone! A home run! - Before landing, the ball went through several

changes in motion. It sped up in the pitchers

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

objects motion stay the same for very long.

Understanding Acceleration

- 1. As the ball falls from the girls hand, how

does its speed change?

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? When it stops and has no direction.

4. How does the velocity of the ball change when

it bounces on the floor?

You can feel acceleration!

If youre 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

SoAcceleration (Final speed Initial speed)

Time

Calculating Acceleration

- 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?

What information have you been given? Initial

speed 4 m/s Final Speed 22 m/s Time 3 s

Calculating Acceleration

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 cars average acceleration is 6

m/s2.

Graphing acceleration

S P E E D

Object accele-rates

Object decelerates

Object moves at constant speed

T i m e

Now You TryA roller coasters velocity at

the top of the hill is 10 m/s. Two seconds later

it reaches the bottom of the hill with a velocity

of 26 m/s. What is the acceleration of the

coaster?

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

objects 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.

Acceleration Problems

- A roller coaster is moving at 25 m/s at the

bottom of a hill. Three seconds later it reaches

the top of the hill moving at 10 m/s. What was

the acceleration of the coaster? - Initial Speed 25 m/s
- Final Speed 10 m/s
- Time 3 seconds
- Remember (final speed initial speed) time is

acceleration. - (10 m/s 25 m/s) 3 s -15 m/s 3 s -5

m/s2 - This roller coaster is decelerating.

- A cars velocity changes from 0 m/s to 30 m/s in

10 seconds. Calculate acceleration. - Final speed 30 m/s
- Initial speed 0 m/s
- Time 10 s
- Remember (final speed initial speed) time is

acceleration. - (30 m/s 0 m/s) 10 s 30 m/s 10 s 3 m/s2

- A satellites original velocity is 10,000 m/s.

After 60 seconds it s going 5,000 m/s. What is

the acceleration? - Remember (final speed initial speed) time is

acceleration. - Final speed (velocity) 5000 m/s
- Initial speed (velocity) 10,000 m/s
- Time 60 seconds
- (5000 m/s 10,000 m/s) 60 s -5000 m/s 60 s
- -83.33

m/s2 - This satellite is decelerating.

- If a speeding train hits the brakes and it takes

the train 39 seconds to go from 54.8 m/s to 12

m/s what is the acceleration? - Remember (final speed initial speed) time is

acceleration. - Final speed 12 m/s
- Initial speed 54.8 m/s
- Time 39 s
- 12 m/s 54.8 m/s 39 s -42.8 m/s 39 s
- -1.097

m/s2 - This train is decelerating.