10 Static > Sliding > Rolling FrictionStatic FrictionResistance to the start of motionSliding FrictionResistance to one object sliding over another objectRolling FrictionResistance to one object rolling over another objectAbout times less than Static/SlidingStatic > Sliding > RollingFluid FrictionAir ResistanceMoving through water
11 Gravity Force that acts between any two masses Only significant when one of the objects is very large (Earth, Sun, etc.)Pulls objects together (attractive force)Force of Gravity is also called weightActs downward toward center of EarthUsed balanced by some other forceSupport force from ground, chair, etc.asdf
12 Falling Objects Gravity accelerates objects downward Air resistance acts opposite to gravity and slows down the accelerationAir resistance gets greater with velocityEventually if falling so long that air resistance balances gravity you will reach terminal velocityTerminal Velocity – constant velocity of a falling object when the force of air resistance equals force of gravity
14 Projectile MotionAny object that is only under the influence of gravity and air resistance is a projectileIf given some initial forward velocity, projectiles will follow a curved pathCombination of initial forward velocity and downward vertical force of gravity causes it to follow curved path.
15 12.2 Newton’s 1st & 2nd Laws of Motion Is a force required for motion?Aristotle (300 BC)Proposed that force is required to keep an object moving at a constant velocityGalileo & Newton (1500’s-1600’s)Moving objects are that are not experiencing friction or any other force will continue to move indefinitelyWould keep moving forever, if there is no frictionObjects have a natural tendency to stay in motion or at rest
16 Newton’s 1st Law of Motion Objects at rest will stay at rest, objects in motion will stay in motion unless acted upon by an outside forceObjects have a natural tendency to resist changes in their motionInertia – property of matter that resists changes in its motionMass is a measure of inertia….. More mass, more inertia
17 Examples of Inertia Seatbelts Rollercoaster Car dashboard Tennis ball/stringEarth’s rotationHelicopter
18 Newton’s 2nd Law of Motion Acceleration of an object is equal to the net fore acting on it divided by the object’s massAcceleration is proportional to net forceMore force, more accelerationAcceleration is inversely proportional to net forceMore mass, less acceleration𝑎= 𝐹 𝑛𝑒𝑡 𝑚
19 W = mg Weight & Mass Weight – in Newtons Mass – In Kilograms (kg) Weight – Force of gravity acting on an objectMass – How much matter is in an objectA measure of how much inertia an object hasWeight = Mass x acceleration due to gravityW = mgWeight – in NewtonsMass – In Kilograms (kg)Acc of gravity – in m/s2
20 Gravitational force differs on other planets MercuryVenusEarthMarsJupiterSaturnUranusNeptuneGravity at equator (Earth=1)0.38g0.9g1g2.64g0.93g0.89g1.12g
23 Why do astronauts float around inside the international space station? They are falling with the space station around EarthContinuously falling without ever running into anything.Gravity is still pulling them
24 Why do satellites orbit Earth? Satellites are forced to circle the Earth by the pull of Earth’s gravity.To orbit a satellite must be travelling at a very fast speed!Around 17,000 mph or fasterSatellites are falling around the EarthObjects in orbit feel weightlessNot actually weightless
25 12.3 Newton’s 3rd Law Newton’s 3rd Law For every action force there is an equal and opposite reaction forceEqual in magnitude, opposite in directionForces only exist in pairs (Action/Reaction)Can’t have an action without a reaction
26 Action & ReactionAction forces produce the interaction, and the reaction force must be in existence at the same time, have the same size, and be opposite in directionYou apply a 10 N eastward force to wall, wall applies a 10 N westward force to you
27 Stuck in Space??An astronaut in space…not moving with just a spacesuit on and he’s not tethered to the ship. If he is only a few meters away from his ship and there are no other people to help him how could you get back to his spaceship?Oh No!!
28 What’s really pushing you? To accelerate you need an outside force…. You cannot apply a net force to yourself!Something outside of you needs to push you in order to move/accelerateThe astronaut in the previous slide need his tool to push him.
29 Should always be able to identify each action/reaction x
39 Law of Conservation of Momentum The total amount of momentum in a system must stay constant unless an outside net force actsInternal forces cannot change momentumCollisionsIf no outside forces…. Momentum is only exchanged between objects never lostRecoil from gun
41 12.4 Universal ForcesThere are four fundamental forces that exist in the universe that can act across a distance (push/pull things without touching)Strong Nuclear ForceActs on neutrons and protons in the nucleus of an atom to hold them togetherElectromagnetic ForceHolds electrons to the positively charged nucleusWeak Nuclear ForceResponsible for radioactive decayGravityAttractive force that acts between any two massesEvery object in the universe attracts every other object