3Review for test on Monday ForcesDefinition- any push or pull on an objectUnits are NEWTONSIdentificationApplied forcesFrictionGravitational forcesMagnetic, electric forces
4ForcesBalanced forces = when all the forces acting on an object cancel each other outUnbalanced forces = when all the forces do not cancel each other out (more force on object in one direction than in others)
5Net force The combination of all forces on an object For balanced forces Fnet = 0At rest or at constant velocityFor unbalanced forces Fnet ≠ 0acceleration
6Weight, mass Weight = the force due to gravitational pull on an object W = mg g = 10 m/s2 on earthMass = the amount of matter that makes up an objectDifferences? Similarities?
7InertiaIs the measure of an objects resistance to change in its motionDirectly related to the amount of mass
8Newton’s 3 laws!st2nd3rdWhen does an object change its motion (accelerate)?
9Collisions and the laws Be able to use the laws of motion to explain what happens in different types of collisionsFront crashRear crashAt least 2 reasons for head restsDoes the bus and the car exert the same amount of force on each other?Why are people less injured on the bus?
10Collisions and the laws Seat-belt configurationsWhat is wrong with just lap-belts?Why are seat-belts flat and wide?What are uses for EKG’s, MRI’s and Xrays?
11Free body diagramsFBD’s purpose: To visually show how the forces are arranged on an objectComponents of a free-body diagramForcesObjectDirection arrow
12FBD Where do all but the direction arrow originate in the diagram? How are the forces of air resistance or friction drawn on FBD?How is the force of gravity drawn on any FBD?
132nd law problems Using Fnet = ma Units for each part are…? Triangle set-up
14Advanced 2nd law problems #1 Have to use the acceleration equation first then use 2nd law#2 Have to determine Fnet first, then use 2nd law
15ExampleNicole slows down in her BMW from 15 m/s to 3 m/s in 42 seconds. What is the mass of her car if the net force on it is 7312 N?
16Law Universal Gravitation There is a gravitational attraction between any two items that have mass.The amount of the force is related to the mass of each object and the distance their centers are apartMore mass, less distance greater force
17Free FallAny object that moves under the influence of only the force due to gravityThrown, Dropped objectsAcceleration = 10 m/s2 or (9.8)
18Terminal velocity The maximum velocity reached by a dropped object Occurs when the downward gravitational force is matched by the upward force of air resistanceAir resistance depends on surface area and speed of object
19Action and reaction forces Identification in the real worldEqual and oppositeApplied to different objectsMay have different effects
20Momentum A quantity of motion The value of an objects mass times its velocityTo have momentum the object has to be ___________.
21Change in momentumTo change an object’s momentum requires a net force being appliedThe greater the force and the longer the time applied the bigger change in momentumBaseball/softball examplesFender benders vs totaling the car
22Momentum change in a accident The amount of change in momentum is constantChange can be brought about different waysMore time less forceLess time more forceSeat Belts, crumple zones, air bags, Padded dashboards
23Conservation of momentum In a system, momentum can not be created or destroyed, but can be transferredMomentum is direction orientedBilliards balls
2818 Free fall means there is only the force of gravity Weightlessness = no force of gravity19 less force of gravity, so acceleration due to gravity is less than 9.820 when the upward force of air resistance = force of gravity
2932 a kg m/s32 b kg m/s32 c 0 kg m/s32 d 12 kg m/s34 gravitational force is much less (1/16th)39 acceleration would be doubled40 a. Train, b. ball, c. equal, equal but opposite