force & motion. observation observations · pay close attention to the following. · make notes...

FORCE & MOTION

Motion• Observing a displacement of one thing relative

to another.

• Describing Motion

• All motion is Relative

• The object moved in relation to the reference object

or point.

Frame of Reference

• The context or limits of what we are discussing• Helps us have a common scope for discussion

Measurement• Defines a scaled common reference

• Can be replicated

• Is known and referenced

• Quantifies the change in position

• Common measurement scales are:• Standard (English/US)

• Feet, Pounds, etc.• Metric

• Meters, Grams, Liters• Internationally accepted system (SI)

LINEAR MOTIONConcepts: Scalars & Vectors

How Do We Describe “Where”?

• If objects move, how can we describe…– How far?– How much?– What direction?

• “How much” or “How far” is the magnitude of motion

• “What direction” is the direction of motion.

Two different “How Far’s”

• Distance– How far?– Scalar– Only measures path

• Displacement– How far from the start are we now?– What direction is it from the start to finish?– Vector– Measure distance and direction from start point to end

point.

Scalars: Magnitude or Direction

MagnitudeHow big

How much

What quantity

OR

DirectionCardinalDegree

Distance: A Scalar

Distance

Start

Finish

Vectors: Magnitude & Direction

MagnitudeHow big

How much

What quantity

AND

DirectionCardinalDegree

Displacement: A VectorDisplacement Finish

Start

Vector Addition“Connect the dots”

Vector Addition

• “Add” vectors to find the net result of the trip.• Net Displacement: The sum of the vectors

Start

Finish

Net Displacement Vector

Finding “Net Displacement” Using Math

• Add all Vertical vectors• Add all horizontal vectors• Us Pythagorean Theorem

Start

Finish


Start

Finish


Sum of vertical vectors

Sum of horizontal vectors

Net Displacementa2

a

b

b2

c2

RATESSpeed, Velocity, Acceleration

Vectors Are Found Throughout Physics

• There are three basic measureable properties in science– Mass– Distance– Time

• Physicists use these to describe the relationships and properties of an objects and their motions.

Speed• Ratio of distance travelled to time taken

• Distance ÷ Time• Scalar quantity

• No direction• Path is important

Velocity• Ratio of displacement to time taken

• Displacement ÷ Time• Vector quantity• Measured from start point to end point• Disregards path

Comparing Speed and Velocity

Dist. = 24 metersTime = 12 secondsSpeed = 2 m/s

Comparing Speed and Velocity

Disp. = 9 meters ENETime = 3 secondsVelocity = 3 m/s ENE

Science Problems“What’s your problem with problems?”

Speedy Velocity Problems“How to work science problems”

Jimmy the Frog hops around his pond.

His hop-o-meter says he has travelled

36 meters. The sundial says it only

took him 20 minutes.

• What was Jimmy’s speed?

How to work science problems

Step 1: Identify your variables (with units!)Jimmy the Frog hops around his pond. His hop-o-meter says he has travelled 36 meters. The sundial says it only took him 20 minutes.

• What was Jimmy’s speed?

Distance: 36 metersTime: 20 minutes

Speed: ???

Distance:36 metersTime: 20 minutesSpeed: ???


Step 2: Write down the equation

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒


Step 3: Change the equation to find the missing variable


SpeedWhat do I need to find?

No

What does the equation solve for?

Do I need to change the equation?

Speed


Step 4: Substitute variable values into formula.


𝑆𝑝𝑒𝑒𝑑=36𝑚20𝑚𝑖𝑛 .



Step 5: Do (and show!!!) your work


=





=


Step 6: Identify your answer

Speed = 1.8 m/min.





=

Speed = 1.8 m/min.

ACCELERATIONIt’s all about change

Acceleration· Ratio of change in velocity to time

· (Displacement ÷ Time) ÷ Time

· Vector quantity

· A change in velocity (direction or magnitude) constitutes

acceleration

GRAPHING MOTION

Dis

tanc

eDistance/Time or Speed Graphs

Speed3.5

3

2.5

(m)

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Distance/Time or Speed GraphsSpeed

3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Dis

tanc

e(m

)


2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Dis

tanc

e(m

)


12

10

8

6

Object 14

2

01 2 3 4 5

Time (s)

Dis

tanc

e(m

)

Displacement/Time or Velocity GraphsVelocity

3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Dis

plac

emen

t(m

)


1.2

1

0.8

0.6

Object 10.4

0.2

01 2 3 4

Time (s)

(m)

Dis

plac

emen

t


3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

(m)

Dis

plac

emen

t


14

12

10

8

6

4

2

0

Object 1

1 2 3 4 5 6Time (s)

(m)

Dis

plac

emen

t

Vel

ocity

(m

/s)

Velocity/Time (Acceleration) GraphsAcceleration

3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Velocity/Time (Acceleration) GraphsAcceleration

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Vel

ocity

(m

/s)

Momentum

Physical Properties of Objects

Innate Properties• Mass• Speed• Size• Density• Color

Derived Properties• Density• Speed• Weight

Observations on Objects in Motion

• Move in a straight line– Unless something pushes them off that line

• Speed wants to remains constant– Less friction is less loss of “speed”

• Massive objects are harder to move– Need more push to move


• If a moving object hits a non-moving object, the non-moving object is set in motion and the speed of the first moving object is reduced.

• How?• Is there a relationship of properties that may

explain this?


What properties of objects seem to be involved?• Speed • MassWhat should we call this Speed-Mass property?• Momentum

𝑀𝑎𝑠𝑠×𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦=𝑀𝑜𝑚𝑒𝑛𝑡𝑢𝑚

Objects & Momentum

𝑀𝑎𝑠𝑠×𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦=𝑀𝑜𝑚𝑒𝑛𝑡𝑢𝑚

Newton’s Laws

Newton’s First Law

• An object will retain it motion unless an outside force acts upon it.

• Inertia: The resistance to movement of an object relative to its mass.

Newton’s Second Law

• An object will accelerate if an unbalanced force is applied to it.

𝑭𝒐𝒓𝒄𝒆=𝒎𝒂𝒔𝒔×𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏

𝑭=𝒎×𝒂

Newton’s Third Law

• All forces between two objects exist in equal magnitude and opposite direction

Weight of Object

Normal Force of Object

END OF MOTIONLECTURE

force & motion. observation observations · pay close attention to the following. · make notes...

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