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Physics … Force & MotionPowerPoint Presentation

Physics … Force & Motion

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Physics… Force & Motion

FORCE…

- “Any influence that can cause a body to be accelerated. It is measured in NEWTONS.”
- A Newton is the force needed to accelerate one kg one meter per second per second
- A push or pull exerted by an object to/on another object

FORCE cont…

- Always occurs in pairs (Sometimes called Agent & Receiver)
- It can alter the shape or motion of an object
- It is represented by arrows that show direction and size

Demos

- Rolling Ball
Shows Acceleration

- Push – Pull; Pushing a closed door; standing on the floor
All show that forces occur in pairs

- Clay ball
Shows how force is required to change shape

- Tennis ball
Change of shape- Elasticity

- Pushing on a table
Forces occur in pairs; Net Force

- Tennis Ball
- http://www.youtube.com/watch?v=sxS-m9CRu34
- Rubber Ball
- http://www.youtube.com/watch?v=N8gxND1kX6k

- Read the biography of Sir Isaac Newton
- Find a Partner
- Decide who will go first

Isaac Newtonb: 25 Dec 1642 d: 31 March 1727

Principia MathematicaPhilosophiae Naturalis

- “Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.”
- Sometimes called the Law of Inertia

What isInertia?

- “The sluggishness or apparent resistance a body offers to changes in its state of motion”
- The larger the mass, the larger its inertia
- A body with less mass is easier to accelerate
- A body with more mass is harder to accelerate

Demo

- Tennis Ball and Cup
Tennis ball has inertia; Newton’s First Law

- http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/
- http://www.youtube.com/watch?v=WOvwwO-l4ps

Demos:http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- Ping pong ball
Small inertia; easy to move & stop

- Bowling ball
Larger inertia; hard to move & stop

- Granny
Small inertia; easy to move & stop

- Mack Truck driven by Granny
Larger inertia; hard to move & stop

Masshttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- Defined as “The quantity of matter in a body”
- It is the measure of Inertia
m = mass; F = force; a = acceleration

m = F/a

F = m(a)

a = F/m

Momentumhttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- The product of MASS and VELOCITY
- It is inertia in motion
- Are you afraid of a piece of grass?

Straw (grass) Through Woodhttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

Small mass, great acceleration

Demos:http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- One Ounce Projectile
A small mass accelerated at high velocity can be produce a lot of force

- Newton’s Jar
Momentum

- Car on a ramp
Momentum

- Eeyore on a car on a ramp
Momentum; inertia in motion

Conservation of Momentumhttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- All energy stored in a moving object is not lost, but only changes form
- This is just like “Energy cannot be created nor can it be destroyed, it can only change form” (Stated by: Albert Einstein; Phillip Morrison, Mr. Watts…)

Demos:http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- Newton’s Cradle
Conservation of Momentum

http://www.youtube.com/watch?v=7_AiV12XBbI&safety_mode=true&persist_safety_mode=1&safe=active

- Swinging Rock
Potential and Kinetic energies; Conservation of Momentum

Mass in a Circular Motion http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- When object moves in circular path it has a property called Rotational Inertia
- AKA: Gyroscopic Inertia

Circular Motion con’t…http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- “An object rotating about an axis tends to remain rotating about that same axis unless it is interfered with by some external force.”
- This definition is similar to Newton’s First Law of Motion

Rotational Inertia Demos:http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- Bicycle tire
- Gyroscope
- Top
- Frisbee
- Football
- Moment of Inertia
- X-Zylo

Angular Momentumhttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- A measure of an object’s rotation about a particular axis
- For an object small compared to the radial distance, it is the product of mass, velocity and radius
- It is the measure of the rotational property of motion
- It is always perpendicular to the centripetal force

Angular Momentumhttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

Demoshttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/:

- Rolling objects
- Washer on a string
- Slingshot (old-fashioned!)
- Bucket with water spun in vertical circles
- Q: What holds the water in the bucket?
- Spin cycle of washing machine
- “Whizzer”
- Brendan on the Scrambler

Carnival Ride Know-Howhttp://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/

- It’s better to take the OUTSIDE seat of the car if you’re riding alone
- If you’re riding with someone else, take the INSIDE seat

- The following formula is similar to those for Newton’s First Law, but deals with mass in motion in a circular path:
mvr = mvr

… The mass is not affected by a smaller radius, while velocity is…

What happens in this situation? First Law, but deals with mass in motion in a circular path:

m v r = ? v r

Demo First Law, but deals with mass in motion in a circular path:

- Spinning on a chair with weights
- Arms Out?
- Pulling arms in?

Centripetal Force First Law, but deals with mass in motion in a circular path:

- A center-seeking force that causes an object to follow a circular path.
- “Any force that is directed at right angles to the path of the moving body and produces circular motion.”

Centrifugal Force First Law, but deals with mass in motion in a circular path:

- A fictitious outward force due to rotation
- It is a reaction to centripetal force but there is no agent, therefore it is experienced relative to position
- What we are really experiencing is ANGULAR MOMENTUM!

Newton’s Second Law First Law, but deals with mass in motion in a circular path:

Law #2

- The acceleration of a body is directly proportional to the net force acting on the body and inversely proportional to the mass of the body and is in the direction of the NET FORCE

2 First Law, but deals with mass in motion in a circular path:nd Law Formulas

- You’ve seen these before:
- a = F/m
- F = m (a)
- m = F/a

What is the acceleration of these? First Law, but deals with mass in motion in a circular path:Acceleration is Inversely Proportional to mass…

5 N

Acceleration = 6 kph

Acceleration = ?

5 N

5 N

Acceleration = ?

Solutions First Law, but deals with mass in motion in a circular path:Acceleration is Inversely Proportional to mass…

5 N

Acceleration = 6 kph

Mass is doubled so

a/ 2 = 3 kph

5 N

Mass is tripled so

a/3 = 2 kph

5 N

Acceleration is First Law, but deals with mass in motion in a circular path:Directly Proportional to force…

5 N

Acceleration = 6 kph

10 N =

(2 x f)

Acceleration = 12 kph

15 N =

(3 x f)

Acceleration = 18 kph

What if I want the Acceleration to be the same for all these bodies?Acceleration is Directly Proportional to force…

5 N

Acceleration = 6 kph

10 N =

(2 x f)

Acceleration = 6 kph

15 N =

(3 x f)

Acceleration = 6 kph

Newton’s Third Law bodies?

3rd Law

- “Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first”
- For every action, there is an equal and opposite reaction
- You cannot touch without being touched

Demo bodies?

- Syringe with water
- Rocket Balloon
- Beaker of Water on Balance

Common Forces bodies?

- Gravitational – non contact
Every object exerts an attractive force on every other object

- Buoyancy - contact
The tendency to float in a fluid

- Friction - contact
The resistance to motion where two objects touch

Common Forces bodies?

- Magnetic – non contact
The repelling or attraction of a magnet and ferromagnetic material

- Elastic - contact
Ability to spring back to its original size, shape, or position after being stretched, squeezed, flexed, expanded, etc.

- Electrical – non contact
Flow or gathering of a negative charge by electrons

Other Physics concepts of interest: bodies?

- ENERGY
The quality of an object that enables it to do work

- Power
WORK/ TIME

Potential Energy bodies?

- The stored energy that a body possesses because of its position with respect to other bodies

Kinetic Energy bodies?

- The energy of motion
- Kinetic Energy = 1/2 mv2

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