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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 ….

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Physics force motion
Physics… Force & Motion


Force
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
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
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


Paired Verbal Fluency

  • Read the biography of Sir Isaac Newton

  • Find a Partner

  • Decide who will go first


Isaac newton b 25 dec 1642 d 31 march 1727
Isaac Newtonb: 25 Dec 1642 d: 31 March 1727

Principia MathematicaPhilosophiae Naturalis



Law #1:

  • “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 is 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



Demos1
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


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

Small mass, great acceleration


Demos2
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 momentum
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…)


Demos3
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
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
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
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 momentum
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/


Demos4
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 how
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



What happens in this situation
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
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
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
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 nd law formulas
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 acceleration is inversely proportional to mass
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 acceleration is inversely proportional to mass
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 directly proportional to force
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
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
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 forces1
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
Other Physics concepts of interest: bodies?

  • ENERGY

    The quality of an object that enables it to do work

  • Power

    WORK/ TIME


Potential energy
Potential Energy bodies?

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


Kinetic energy
Kinetic Energy bodies?

  • The energy of motion

  • Kinetic Energy = 1/2 mv2


As an object falls its energy transforms from all potential to all kinetic
As an object falls, its energy transforms bodies?from all Potential to all Kinetic

P

K

K

P


At which point will the potential and kinetic be equal
At which point will the bodies?Potential andKineticbe equal?

P

K

Right here! ½ way

K

P


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