Forces F n Definition a push or pull

Forces (F) n Definition: a push or pull that has the ability to cause a change in motion n. Standard unit is the Newton

Where did this unit come from? ? Sir Isaac Newton n English physicist and mathematician n Laws of Motion and Gravitation n Invented Calculus All before the age of 30!

Types of Forces q. Forces cause motion q. Motion depends on net force NET means “total” or “sum” Forces can be balanced or unbalanced

Balanced Forces q. Equal in size q. Opposite in direction q. No motion occurs! (equilibrium) Like a tie in an arm wrestling match! p. 51

Unbalanced Forces q. Unequal in size q. Can be in the same direction OR in opposite directions q. Forces must be unbalanced to cause a change in motion

As a box is sliding down a ramp, a 10 N force of gravity is pulling the box down the ramp while a 2 N force of friction acts to stop the box. What is the net (total) force accelerating the box down the ramp? (Magnitude and Direction!!) 8 N to the Right

What is the Net Force? ? ? 1 N 3 N Fnet = 1 N – 3 N = -2 N Fnet = 1 N +1 N 1 N = +2 N Fnet = -1 N – 1 N 1 N = -2 N

Friction a force that goes against motion Four Types of Friction: 1. Air friction (Resistance) 2. Viscous friction 3. Sliding friction 4. Rolling friction

1. Air Friction Also called Air resistance (aerodynamics reduce the air friction) Ex - falling objects or airplanes

2. Viscous Friction Moving through a liquid, or fluid q. Ex. - swimming

3. Sliding Friction Two surfaces rub against one another Ex - rubbing hands or clapping Oil and other lubricants help reduce friction.

4. Rolling Friction An object rolls over a surface Ex – any object with wheels A_World_Without_Friction. asf

Gravity q. Def - A downward force that causes objects to accelerate to the center of mass Gravity causes all falling objects to accelerate at the same rate. (9. 8 m/s 2)

n. Free Fall Tower Gizmo

n Apollo 15 Hammer and Feather Drop n Mythbusters Recreates Apollo 15 Drop

Mass (g) Amount of matter inside of an object Is NOT Weight (N) A measure of the force created as your mass responds to gravity

Calculating Weight Formula: Force of Weight (N) Mass (Kg) g m = Fw Gravity = 9. 8 m/s 2 p. 53

q. Let’s look at how mass, weight, and gravity are related. q. Mass DOES NOT change, but your weight will change if there is a change in gravity

n What would happen to your weight if you were on the Moon? n What would happen to your mass if you were on the Moon?

n. Weight and Mass Gizmo

Law of Universal Gravitation Newton said that gravitational force depends on 2 things: things The DISTANCE from the center of gravity LESS gravitational force MORE gravitational force The MASS of the objects The yellow object has more gravitational force than the red object because the yellow object has more MASS

The pull of gravity also keeps satellites orbiting around the Earth The mass of the moon is much smaller than the mass of the Earth, so the Moon is controlled by the gravitational pull of the Earth.

Does the moon’s gravitational pull effect the Earth? Yes, the moon’s gravity is large enough to actually pull water out of the ocean from space… Well, not quite that much. . . just enough to create motion of the tides.

n As you move further from the center of the Earth, the force of gravity DECREASES. n Where would you weigh less, in Galveston or in Denver? n Denver is the “Mile High City”; the force of gravity is less. Therefore, the force of gravity would be less because it is further away from the center of the Earth, and you would weigh slightly less. Gravity Song!

Newton’s First Law (Law of Inertia) n An object at rest stays at rest and an object in motion keeps its same motion, UNLESS an outside force acts on it. Teenage Terms – Objects will keep doing what they are doing unless an outside force changes that!

n. Def. Inertia - The tendency of an object to resist any change in motion n You must overcome inertia to start or stop motion n Depends on the mass of the object As mass , inertia will

Which object has the greatest amount of INERTIA? ? n. Pencil n. Baseball n. Bowling Ball n. Ping Pong Ball

n. INERTIA is what causes a person (or anything else in the) involved in a head-on collision to continue moving forward at the same speed that the car was traveling, until some outside force causes it to stop (i. e. seatbelt, windshield, etc. )

What’s wrong with this picture? ?

Inertia

Other Examples of st 1 n Card Tricks n Dishes and table cloth n Collisions and seatbelts n. Crash Test Dummies n Bike Ramp Crash n First Law, Inertia, and Friction Video Law

Newton’s nd 2 Law (F = ma) n The acceleration of an object is directly proportional to the force acting on it and inversely proportional to its mass. F, a (direct relationship) m, a (inverse relationship)

Force and Acceleration are Directly Proportional F 2 N a F=ma 2 N =(1 kg)a a= 2 m/s 2 4 N F=ma 4 N =(1 kg)a a= 4 m/s 2

Mass and Acceleration are Inversely Proportional m, a (inverse relationship) F = ma 1 N = (1 kg) a a = 1 m/s 2 F= ma 1 N = (2 kg) a a = 0. 5 m/s 2

Solving nd 2 Law Problems Use the formula: Unit for Force is Newtons (N) Unit for Mass is kilograms (kg) Unit for Acceleration is m/s 2

Solving 2 nd Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s 2 ? Variables Formula Plug-n chug Answer F= ? m=5 kg a= 2 m/s 2

Solving nd 2 Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s 2 ? Variables Formula Plug-n chug Answer F= ? F = ma m=5 kg a= 2 m/s 2

Solving 2 nd Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s 2 ? Variables Formula Plug-n chug Answer F= ? F = ma F =(5 kg)(2 m/s 2) m=5 kg a= 2 m/s 2

Solving 2 nd Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s 2 ? Variables Formula Plug-n chug Answer F= ? F = ma F =(5 kg)(2 m/s 2) m=5 kg a= 2 m/s 2 F= 10 N

Solving 2 nd Law Problems n Explains why you can throw a baseball further than a bowling ball n Braking force required to stop a Volkswagen vs. a dump truck n Why a Mustang accelerates faster than a bus

1. What is the acceleration of a 500 kg ball rolled with a force of 3. 6 N? 2. A rollercoaster accelerates at a rate of 30 m/s 2. If the rollercoaster has a mass of 10, 345 kg, what size force must be applied? 3. What is the mass of a tanker

rd 3 Newton’s Law (Action/Reaction) n Whenever one object exerts a force on another (action), the second object exerts an equal and opposite force (reaction) on the first. n All forces come in pairs.

Newton’s Third Law: For every action there is an equal and opposite reaction Look at the picture below: What is the action? The gases push downward out of the rocket What is the reaction? The the rocket is pushed upward by the gases

Examples of n Leaning on wall rd 3 Law (action: you push on wall, reaction: wall pushes back on you) n Firing a cannon (action: cannon pushes on cannon ball, reaction: cannon ball pushes back on cannon) n Walking (action: you push on the earth, reaction: the earth pushes back on you) n Space Shuttle taking off (action: rocket thrusters push down, reaction: the space shuttle travels upward)

America’s Funniest Videos n Dorm Chair Hit (Newton’s Third Law & Conservation of Momentum) n http: //abc. go. com/primetime/afv/inde x? pn=videoplayer&id=363529

An object will maintain a constant state of motion until acted upon by an “unbalanced” force. This law shows how force, mass and acceleration are related. Force = mass x acceleration For every action there is an equal and opposite reaction

Calculating Momentum • Unit: kg m/s Formula: Mass (Kg) = mv p Momentum (Kg -m/s) Velocity (m/s)

n. Will two moving objects with the same mass always have the same momentum? ? MASS = 100 kg V = 1 m/s (About 220 lbs) V = 3 m/s NO!! Their velocities need to be considered!!

n 3 Examples of Momentum n. Momentum of a Marble in a Bowl

Law of Conservation of Momentum Total amount of momentum can not change

What is the momentum of a blackbird with a mass of 0. 04 kg flying at 19 m/s?

A meteorite has a momentum of 100 kg-m/s. If the velocity is 1000 m/s, what is its mass?

A frog with a mass of 0. 9 kg hops with a momentum of 10. 8 kg-m/s. What is its speed?