# Newton’s Third Law: Impulse & Momentum “How many horses had to die for this stupid, itchy wig?” a momentous topic.

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Newton’s Third Law: Impulse & Momentum “How many horses had to die for this stupid, itchy wig?” a momentous topic

“For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica

Is known as the “Impulse-Momentum” theorem, where Change in momentum Impulse

“For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica Inertia in motion** Product of mass & velocity Momentum? Huh? **For subatomic-sized particles moving really, really fast (~90% of light speed), momentum is defined differently. It’s impossible to determine BOTH position and momentum at the same instant in time because of some freaky mathematics; hence, we have Heisenberg’s Uncertainty Principle.

“For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica Heisenberg may have slept here... but, for relatively large objects (like molecules) that are moving fairly slowly (<0.9c), the classical definition of momentum works just fine, and is much less complicated.

 p = m  v +  mv Or BOTH may change! “For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica For momentum to change, the mass can change, the velocity can change, pp p = mv  m*v  m*  v

These two canoeists (each of mass 60 kg) propel their canoe (30 kg) at 5 m/s towards an unseen rock on this pond. After the 0.5-s collision, the canoe moves back at 1 m/s. This canoe can withstand a force of 1500 N without puncturing. Big rock just under here Will the canoe break? What is the change in momentum of the canoe/passengers?

“For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica  p = m  v  p = (150 kg)(6 m/s)  p = 900 kg m/s -5 m/s 1 m/s

“For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica F = 1800 N

“For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica A 75-kg driver is traveling at 100 m/s when his car comes to a sudden stop. The driver is not wearing a seatbelt. He collides with the steering column for 0.005 s. The human body can withstand about 9 times the weight of the body as impact force. Has this driver committed suicide-sans- seatbelt?

“For every action, there exists an equal and opposite reaction.” - Isaac Newton, Principia Mathematica A 75-kg driver is traveling at 100 m/s when his car comes to a sudden stop. The driver is wearing a seatbelt. He collides with the steering column for 1.2 s. The human body can withstand about 9 times the weight of the body as impact force. Has this driver committed suicide-sans-seatbelt? This crash occurred in Oahu; yes, the driver was wearing a seat belt AND WALKED AWAY!

Many mooses’ mass may be more than your Maserati’s mass. This moose’s mass is 680 kg, and it is initially moving at 9 m/s. If the collision lasts for 0.5 s, how much force is sustained by the car?

Water leaves a fire hose at a rate of 125 kg/s with a speed of 200 m/s and strikes a wall, which stops it. (We’re ignoring any splashing back.) What is the force exerted by the water on the wall? FYI: Fire hoses were used in the 1960’s to break up peaceful civil rights demonstrations.

Calculate the force exerted on a rocket, given that the propelling gases are expelled at a rate of 1000 kg/s, with a speed of 60,000 m/s (at takeoff).

Your assignment for next time:  pp. 83+: RQ 1-8; T&E 1,3-12,15

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