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• • • • • • • • • • • • • • • • • Motion & Forces Lesson 3 • Newton’s Third Law Newton’s Third Law of Motion When one object exerts a ___________ on a second object, the second object exerts an ____________ but _______________ force on the first. • Newton’s Third Law Problem: How can a horse pull a cart if the cart is pulling back on the horse with an ____________ but ___________ force? Aren’t these “______________ forces” resulting in no acceleration • Newton’s Third Law forces are equal and opposite but act on ________________ objects they are _______ “balanced forces” the __________________ of the horse depends on the ___________________ acting on the horse • Action and Reaction When a ________________ is applied in nature, a reaction force occurs at the same time. When you jump on a trampoline, for example, you exert a _____________ force on the trampoline. Simultaneously, the trampoline exerts an equal force ____________, sending you high into the air. • Action and Reaction Forces Don’t Cancel According to the third law of motion, action and reaction forces act on ______________ objects. Thus, even though the forces are ____________, they are not balanced because they act on different objects. • Action and Reaction Forces Don’t Cancel For example, a swimmer “_________” on the water, the “___________” of the water pushes the swimmer forward. Thus, a net force, or _____________ force, acts on the swimmer so a change in his or her motion occurs. Rocket Propulsion In a rocket engine, burning fuel produces hot gases. The rocket engine exerts a force on these gases and causes them to ________________ out the back of the rocket. By Newton’s third law, the gases exert a force on the rocket and _____________ it forward. • • • • • • • Newton’s Third Law Action-Reaction Pairs The hammer ______________ a force on the nail to the right. The nail exerts an equal but _______________ force on the hammer to the left. • Momentum A moving object has a property called momentum that is related to how much force is needed to change its _________________. The _________________ of an object is the product of its mass and velocity Momentum is given the symbol ____ and can be calculated with the following equation: • Momentum • • • Momentum _________________ of motion p: ________________ (kg·m/s) • m: ____________ (kg) • v: __________________ (m/s) • • • • • • • Force and Changing Momentum By ___________________ these two relationships, Newton’s second law can be written in this way: _____________________________________________ In this equation __________ is the final momentum and ___________is the initial momentum • Law of Conservation of Momentum The momentum of an object doesn’t change unless its mass, ________________, or both change. Momentum, however, can be ____________________ from one object to another. The law of conservation of momentum states that if a group of objects exerts forces only on each other, their total momentum _______________ change. • Law of Conservation of Momentum The results of a collision depend on the _____________________ of each object. When the first puck hits the second puck from behind, it gives the second puck momentum in the same __________________. • When Objects Collide If the pucks are speeding toward each other with the same speed, the total momentum is _________________. Newton’s Third Law • • Action-Reaction Pairs Both objects accelerate. • The amount of acceleration depends on the mass of the object • • • • • • Conservation of Momentum Law of Conservation of Momentum The total momentum in a group of objects doesn’t change unless outside _______________ act on the objects. • Conservation of Momentum ______________ Collision KE is conserved _____________ Collision o • KE is not conserved • Momentum Find the momentum of a bumper car if it has a total mass of 280 kg and a velocity of 3.2 m/s given work answer: • • Momentum The momentum of a second bumper car is 675 kg·m/s. total mass is 300 kg? given answer: work What is its velocity if its • • Conservation of Momentum A 5-kg cart traveling at 1.2 m/s strikes a stationary 2-kg cart and they connect. Find their speed after the collision. given work answer: • • Conservation of Momentum A 50-kg clown is shot out of a 250-kg cannon at a speed of 20 m/s. What is the recoil speed of the cannon? given work answer: • • Conservation of Momentum So…now we can solve for velocity given answer: work