You must have a force to change motion Things will continue in motion unless another force acts on the object Force = push or pull, any action that can change the acceleration (or motion) of an object.

In 1687, Sir Issac Newton developed Laws of Universal 3 Motion Essentially, he was the first person to mathematically describe motion or gravity correctly.

 An object at rest will stay at rest, and an object in motion will stay motion unless a force acts on it.  Force is needed to change motion in  Forces could be a gravity, friction, push, a pull, a kick, wind resistance, etc…

 Object stays in motion (the crash test dummy) stays in motion until an outside force acts on it (the windshield).  Just because the car stops, doesn’t mean the dummy will stop instantly  Dummy keeps moving until a seatbelt, or airbag, or steering wheel (etc…) stops it

 And this one is just funny…

 Inertia – property of an object to resist change in motion or acceleration a  The inertia of an object cannot  It depends on mass of the object  Large mass = Large Inertia = Hard to stop change

 We already know:  Force causes acceleration  Mass resists acceleration  SO… SO…  Force = Mass x Acceleration  F=MA

Force is measured in Newtons In science talk: a force of 1 N causes a 1kg object to accelerate at a rate of 1 m/s 2 1kg * 1 m/s 2

PRACTICE PROBLEM:  What is the acceleration of a boy on a skateboard if the net force acting on the boy is 15N, assuming the total mass of the boy and the skateboard together is 58kg?

PRACTICE PROBLEM:  What is the mass of an object if a force of 34N produces an acceleration of 4.0 m/s 2 ?

 The more mass you have, the bigger the force required to move you  The less mass you have, the less force required to move you.

 For every action, there is an and opposite reaction.  Forces always act in pairs  Forces are equal and opposite equal 3 rd  Newton’slaw includes theforces acting on two objects instead one.  The forces DO NOT cancel out because they are acting on different objects.  Can you think of an example of this in real life? ofjust

 Dog walking on a float in the pool (2 min)  p://  Jumping out of a boat (2 min)  p:// 3 rd  Newton’sLaw: USC Lecture (4 min)  p://  DEMO – “Bottle rocket”

 Balloon is blown up with air, and then let go. The balloon flies forward as long as air is exiting the balloon?  Newton’s 3rd Law  A bowling ball, once thrown down a greased up bowling lane, will continue traveling unchanged until it hits the pins or the backstop. 1 st  Newton’sLaw  Cannon fires a cannonball. The cannon moves backward as it is fired, while the cannonball shoots forward. 2 nd  Newton’sLaw

Weight and Mass

Life on Mars So imagine that you are on planet Mars. Is the amount of matter that makes you up different? Is the force pulling you downward different?

Weight Weight – Theforce pulling down on an object created by earth’s gravity (9.8m/s 2 ) Weight is a FORCE Therefore, units = NEWTONS Your Weight will be different on Earth and Mars Earth’s gravity = 9.8m/s 2 Moon’s gravity = 1.6m/s 2 Weight changes with gravity (N)

Calculating Weight Formula: Symbols Units Force Weight = Mass * Gravity Fw (N ) = m = (kg) * g (m/s 2 ) Rememberto use Newtons NOTPounds sincewe are Scientific. (1 N = 2.2 lbs) Look Familiar? Formula: Symbols Formula: Symbols Force Weight Fw Force F ======== Mass * Accel due to Gravity m* g Mass * Accel m*A

Calculating Weight Example: Earth (9.8m/s 2 ), what is your Ifyou have a mass of 22kgonweight? 22kg * 9.8m/s kg*m/s N Fw ====== Ifyou have a mass of 22kg what is your weight? onMars (with1/3thegravityofEarth), 22kg * ((9.8m/s 2 ) * 22kg * 3.27m/s kg*m/s N Fw ======== (1/3))

Mass Mass – amount up an object. Units = kg ofmatterthatmakes Your Mass will or Mars. bethe same on Earth You have the same amount of matter everywhere.

Weightvs.Mass Weight is measure of acting on your mass the force of gravity Weight will be different everywhere Units = N (because it is a FORCE) Mass is the same everywhere, regardless of gravity Mass will always remain the same Units = kg

Friction If gravity is always pulling us down (or if we are moving) we are always going to be in contact with something. Friction is a force that results from the relative motion between AKA: The force motion because objects that works against and slows the surface of any object is rough

Friction Some friction is useful Walking (friction between ground and foot) Driving (friction between ground and tire) Brakes (friction between brake pad and the disc (attached to wheel) Writing (friction between paper and pen/pencil) Throwing (friction between hand and ball) Some friction is unwanted Overheating in a machine/engine is caused by friction Any moving that slows down when it is not wanted Friction makes moving heavy objects much harder

Recap - Weight, Gravity Gravity pulls everything toward center of earth. 9.8m/s 2 (Accelearation) andFriction Weight is a measure of the forceof gravity pulling on an object’s mass. Friction is a force caused by the relative motion between 2 objects.

Multiple Forces ActingAtAtOnce There will always be MORE than acting on an object at a time. Net force = total of all forces 1force There are 2 options: Balanced forces Equilibrium = all forces on are balanced and no change in occurs Unbalanced forces an object movement Net forces do not equal zero Motion will occur in the direction of the Net Force

Free Body Diagrams - HONORS There is a box on the table. What forces are acting on this box? Weight Gravity pulling down on the box Normal Force Table pushing up What other forces can act on the box? Push to the right (or pull from the right) Friction force In the opposite direction of the push

Free Body Diagrams Identify the value for: Force of Weight: Normal Force: Friction Coefficient: “Push”: -HONORS Is this box moving? If so, which direction unbalanced force? and with what

Free Body Diagrams - HONORS This can be shown 2 different ways: Arrows pointing towards the center of the object Arrows originating from the center of the object.

Multi Equation Problems

Atthispoint,youknowafew equations… p=m*v D=m/V F=m*a s=d/td/t a = (v f -v i )/t Fw =Fw =m*g Do any of theseequations have similarparts?

Sonowwecanusemultiple equationsinoneproblem…  An ice cube, with a density of.93g/cm 3, has a volume of 185cm 3. is thrown with a force of 9.5N, what is the acceleration at which ice cube was thrown? If I am searching for Acceleration, I 2 triangles that have Acceleration. If it the havehave  What have you been given? Density =.93g/cm 3 Volume = 185cm 3 Force = 9.5N Which one would a = (vf – vi)/t F = m * a Iusehere? What are you looking Acceleration = ? for?

Sonowwecanusemultiple equationsinoneproblem…  An ice cube, with a density of.93g/cm 3, has a volume of 185cm 3. If it the is thrown with a forceofof9.5N, what is the acceleration at which ice cubewaswasthrown? If I am solving for acceleration, where do I get my mass from? From Density = Mass /volume Solve for mass using D=m/V, then plug into F=ma. Don’t forget to convert g (from density) to kg (from force)! (This is the only time you will ever have to convert units)

Sonowwecanusemultiple equationsinoneproblem… An ice cube, with a density of.93g/cm 3, has a volume of185cm 3. If it the  is thrown with a force ice cube was thrown? ofof9.5N, whatistheaccelerationatwhich D = m / V.93 g/cm 3  = m / 185cm 3 * 185cm 3 = m m = g CONVERT from grams F = m * a 9.5N = kg * a 9.5N / kg = a (172.05g) tokilograms (.17205kg)  55.88m/s 2 Acceleration= 