2 Action-at-a-Distance Forces What is a Force?Force –Measured in NewtonsChanging Motion-Contact ForcesAction-at-a-Distance ForcesFrictional ForceGravitational ForceTension ForceElectrical ForceNormal ForceMagnetic ForceAir Resistance ForceApplied ForceSpring Force
3 3.1- Forces Forces Net force – Rules for Adding Forces Add forces in the same direction.Subtract forces in opposite directionsForces not in the same directions\ or in opposite directions cannot be directly added together.
8 Let’s Practice If your mass is 70 kg on Earth, what is your weight? A boy weighs 400 N. What is his mass?An astronaut has a mass of 100 kg and a weight of 370 N on Mars. What is the gravitational strength of Mars?
9 Gravity 3.1- Forces Weight and Mass Weight on Earth Finding other Planets
10 3.2- Newton’s Laws of Motion Newton’s 1st Law of MotionNewton’s 1st Law –Break it Down – Things want to keep doing what they are doingInertia –Inertia and MassMass corresponds to an object’s inertiaMore massive objects have more inertia than less massive objects
11 3.2- Newton’s Laws of Motion Newton’s 2nd Law of MotionNewton’s 2nd LawBreak It Down – F=maAcceleration is caused by net forceAcceleration is directly proportional to net forcePush an object, object acceleratesPush an object with twice as much force, then it accelerates twice as muchDirection of acceleration is always the direction of the net force
12 3.2- Newton’s Laws of Motion Newton’s 2nd Law of MotionMass and accelerationMore massive objects are harder to accelerateAcceleration is inversely proportional to massPush a brick, brick acceleratesPush 2 bricks with same amount of force, accelerates ½ as much3 bricks accelerates 1/3 as much
13 3.2- Newton’s Laws of Motion Newton’s 2nd Law of MotionMass and accelerationMore massive objects are harder to accelerateAcceleration is inversely proportional to massPush a brick, brick acceleratesPush 2 bricks with same amount of force, accelerates ½ as much3 bricks accelerates 1/3 as much
14 Let’s Practice!!!With what force will a car hit a tree if the car has a mass of 3,000 kg and it is accelerating at a rate of 2 m/s2?A 10 kg bowling ball would require what force to accelerate it at 4 m/s2?If a helicopter’s mass is 4,500 kg and the net force on it is 18,000 N upward, what is it’s acceleration?
15 3.2- Newton’s Laws of Motion Newton’s 3rd Law of MotionNewton’s 3rd LawBreak It Down - forces always occur in pairs
16 A Simple Rule Helps to Identify Action and Reaction Action: Object A exerts a force on Object B Reaction: Object B exerts a force on Object A
17 Identifying Force Pairs Identify the following Force PairsAction: Enclosed air particles push balloon wall outwards.Reaction: ?Action : Baseball pushes glove leftwardsReaction: ?Action: Shuttle pushes exhaust gases downReaction: ?
18 3.2- Newton’s Laws of Motion Action and reaction forces do not cancel each other outForces only cancel when they act on the same bodyAction-Reaction forces work on different objects
19 3.3- Using Newton’s Laws What happens in a crash? Newton’s 1st Law and Safety BeltsAir Bags in Cars
20 3.3- Using Newton’s LawsNewton’s 2nd Law and Gravitational AccelerationAir ResistanceDepends on size and shapeDepends on speed of objectMore speed, more airresistanceTerminal velocity -
21 3.3- Using Newton’s LawsNewton’s 2nd Law and Gravitational AccelerationFree Fall –WeightlessnessWhat does weightless mean?
22 3.3- Using Newton’s Laws Centripetal Forces Centripetal force- Force acting toward the center of circle
23 3.3- Using Newton’s Laws Force and Momentum P = mv Conservation of MomentumLaw of Conservation of momentumMomentum conserved