Transcript motion
Motion, Momentum, & Centripetal Force Newton’s Laws of Motion • • 1st Law: An object in motion remains in motion & an object at rest remains at rest unless acted upon by an outside force. Inertia: The tendency of an object to resist any change in its motion Newton's 1st Law of Motion in a car crash video clip Car Crashes & Newton’s 1st Law of Motion 1. 2. 3. 1. 2. 3. 4. • 3 collisions occur in a car crash: The car crashes & stops (occurs within 1/10 of a second) The occupant stops (same speed the car was going) The occupants internal organs stop (same speed as car) • 4 ways seat belts help save lives: Keep occupants in the vehicle (not thrown out into traffic/etc.) Keep occupants from hitting hard parts of the vehicle Spread the force over a larger area (reduces pressure) Increases the stop time (seatbelt gives a little) • • Newton’s Laws of Motion 2nd Law: The force of an object is equal to the product of its mass and acceleration. F = m x a (m = F/a or a = F/m) (F = force, m = mass, a = acceleration) (Unit of measure for force is the Newton N) Ex: an object has a mass of 10kg and accelerates at 2m/s2, it needs _20N_ force to do this. 10kg x 2m/s2 = 20N • Mass: The total amount of matter in a substance • As mass increases, inertia increases, and the force needed for acceleration increases. Newton’s 3rd Law of Motion: For every action, there is an equal and opposite reaction. (equal in force, opposite in direction). • Momentum: The product of an object’s mass and velocity. p=mv or mv = p (p=momentum, m = mass, v = velocity) Ex. a 0.5 kg ball thrown at 6 m/s 0.5 kg x 6 m/s = 3 kg · m/s • Impulse: m x v ÷ stop time Ex: a 100 lb person traveling at 50 mph in a car crash hits the dash board in 1/10 second. 100 lb x 50 mph ÷ 0.1 sec = 50,000 lb impulse momentum and impulse video clip • Law of Conservation of Momentum: the total momentum of any group of objects remains the same unless outside forces act on the objects. • Law of Conservation of Momentum Pi = Pf M1V1 + M2V2 = MTVf (40 kg ∙ 10 m/s) + (30 kg ∙ 5 m/s) (400 kg∙m/s) + (150 kg∙m/s) = 70 kg ∙ Vf Pi ÷ MT =Vf 550 ÷ 70 = 7.68 m/s http:// • Centripetal Force: A force that causes objects to move in a circle (center-seeking) • Centrifugal force = center-fleeing centripetal force video clip spinning video clip