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Newton’s 1 st Law of Motion • Objects in motion tend to stay in motion at constant velocity, and objects at rest tend to stay at rest, unless acted upon by an outside force. • The outside force that stops objects that are rolling along is friction. Without friction, the object wouldn’t stop until another force acted upon it. • http: //nbclearn. com/nfl

Inertia! • http: //www. youtube. c om/watch? v=vfnt 8 Sd j 7 cs

Newton’s 1 st Law of Motion • Inertia is the property of matter that resists any change in motion. • • Standing on a bus: When it starts moving, you lose your balance, when it stops you fall forward. When driving in a car, if the road curves, the driver must turn the steering wheel so that the car will follow the curve; the people inside continue to move straight ahead until the seat or walls of the car force them to follow the curve. You are sitting still at a red light and another car hits you from behind. How does a headrest help in this instance? Ex: Tie a string to a small boat and you can pull it – why can’t you pull an ocean liner the same way? • • Both boat and ocean liner are ‘weightless’ as the water is supporting their weight so you don’t have to. The ocean liner has more mass, so it has more inertia. http: //youtu. be/o. Kb 2 t. Ctpv. NU

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• How does changing mass affect the acceleration? • How does changing the force you use, affect acceleration? http: //youtu. be/s. KSPx. Qj. POm 0

Newton’s 2 nd Law of Motion • The 2 nd law says that the acceleration of an object depends on the object’s mass and the size of the force acting on it. • The formula that explains Newton’s 2 nd Law of Motion is • • Force = mass x acceleration (F = ma) OR…… a = F/m • This formula shows you why a boulder and a pebble would fall at the same rate!

Newton’s 2 nd Law of Motion • 1 st law shows you that acceleration and force are related - the 2 nd law explains how they are related. • • http: //nbclearn. com/nfl Stronger forces increase acceleration; • • Kicking an object will cause greater acceleration than flicking it with a finger Larger masses require more force for acceleration • Requires more force to move a truck than it does a car • So, a 750 kg car gets better gas mileage than a 2000 kg truck, at the same acceleration because it takes less force to get it going. • A semi has greater _____. It requires a greater _____ to achieve the same ______ (make it around the corner). What supplies that _____?

Problems A weightlifter raises a 200 kg barbell with an acceleration of 3 m/s 2. How much force does the weightlifter use to lift the barbell? Step 1: Write Knowns Step 2: Write Formula Step 3: Plug Knowns into Formula Step 4: Solve – ensure units carry through

Problems 1. How much force is needed to accelerate a 1000 kg car at a rate of 3 m/s 2? 2. If a 70 kg swimmer pushes off a pool wall with a force of 250 N, at what rate will the swimmer accelerate away from the wall? 3. A dancer lifts his partner above his head with an acceleration of 2. 5 m/s 2. The dancer exerts a force of 200 N. What is the mass of the partner?

Newton’s 2 nd Law Recap • You are riding your bike, pulling a loaded wagon behind you. The wagon suddenly becomes unhitched. • Give one of the two ways you would know this without looking. • Why is it so Hard to Go into Space? https: //vimeo. com/86572593

• http: //nbclearn. com/nfl • 3 rd Law

Newton’s 3 rd Law of Motion • 3 rd Law: For every action there is an equal and opposite reaction; All forces come in pairs • • Push on a wall, it pushes back Airplanes push air out of the engines, the air pushes the plane forward

Newton’s 3 rd Law of Motion • Since they act in opposite directions, do they cancel each other out? Why or why not? • cuz they are not acting on the SAME object! • Ex: In a stalemated tug-of-war both sides are pulling on the same rope so ARE NOT A-R pairs • One team pulls on the rope, the rope pulls back IS an A-R pair

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Newton’s Laws of Motion • Explain the launch of the space shuttle using all three Laws of Motion…….

Momentum • • All moving objects have momentum. Momentum is determined by the mass of the object and the velocity at which it is traveling. Momentum = mass x velocity Can an object with less mass have more momentum than a larger one? • • A 75 kg fullback running downfield and collides with a 125 kg defensive back blocking him, and runs him down. - Why? Is momentum a vector?

Momentum • The law of conservation of momentum, states that the total momentum of any group of objects remains the same unless an outside force acts on the objects. • Ex: Billiards - what is the outside object? • • Once the pool balls start moving, why don’t they just keep moving forever, transferring momentum back and forth to each other? Fireworks……

Momentum • The total momentum of objects that interact must be the same after the interaction as the total momentum before to the interaction. • If one of the objects in a collision speeds up, then the other must slow down. – billiards…. explain.

Momentum • If the system was at rest to begin with (0 momentum), then the momentum of one object moving forward must equal the momentum of the other object moving backward. • Shotgun vs bullet

Momentum • If two skaters are at rest, and one pushes off of the other and slides away at 35 m/s, and the other slides away in the opposite direction at 28 m/s, what is the total momentum of the two skaters?

Practice • What is the momentum of a 920 kg car moving at a speed of 25 m/s? • Which has more momentum, a 250 kg dolphin swimming at 4 m/s or a 350 kg manatee swimming at 2 m/s? • Find the force it would take to accelerate an 800 kg car at a rate of 5 m/s 2. • What is the acceleration of a 0. 15 kg hockey puck struck with a force of 1. 8 N?

Impulse • Impulse changes motion. • To change an object’s motion, you need a push or pull …. . Force • • • http: //www. youtube. com/watch? v=r. XGKys 62 TXw&f eature=related http: //www. youtube. com/watch? v=x. G 9 d. AROIKPQ But the amount of time you apply that force affects the motion as well • • • Toss an egg at a wall = splat Toss an egg into a blanket with give = � Both stop the egg, the blanket extends the time the force is applied

Impulse • Impulse = F (t) • The greater the impulse, the greater the change in motion • • • Hand gun vs shotgun Longer cannon Follow through on swing in baseball or golf vs bunt/putt Car crash Jumping from a height – straight legged vs bending legs when land Quick jab in boxing

Impulse • Impulse is greater when objects bounce. • It takes more impulse to stop an object and throw it back than it does to just stop it • • Weight ball Water wheel during the gold rush – flat paddle vs ushaped • • The u-shape caused the water to hit and do a u-turn or bounce back making the paddles much more effective Sky diving