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Transcript
Forces • Def – an action exerted on an object to change the object’s state of motion (resting or moving) – Magnitude and direction – Units: Newtons (N) • Net force – total force on an object – When there is a net force on an object, the object accelerates in the direction of the net force – If net force = 0, then the object does not move Balanced forces • Net force = 0, no movement – Forces are balanced – An object standing still will not move – An object moving will not stop Unbalanced Forces • Net force is greater than zero, unbalanced force – Object will move Friction • Force that opposes motion between two surfaces that are in contact 2 types – Static – friction between two forces at rest, initial friction an object must overcome – Kinetic – friction between two moving objects • Static friction is usually greater Newton’s Laws • He was born the same year that Galileo died • Newton had ideas about motion, which he called his three laws of motion – Also had ideas about gravity, the diffraction of light, and forces • Physics and Math • Helped create Calculus First Law • Law of inertia – An object at rest will stay at rest and an object in motion stays in motion unless acted on by an external force • Inertia – tendency of an object to stay at rest or stay in motion – Mass is a measure of inertia – Small mass = less inertia • Seatbelts Second Law • The unbalanced force acting on an object equals the object’s mass times its acceleration – F=ma – Force is measured in Newtons (N) • 1 N = 1 kg x 1 m/s2 Q: What is the force necessary for a 1600 kg car to accelerate forward at 2.0 m/s2 ? 2nd Law Problem Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s2 . Using Newton's Second Law, compute how much force Mike is applying to the car. Third Law • For every action there is an equal and opposite reaction – Opposite in direction. – Whenever an object pushes another object it gets pushed back in the opposite direction equally hard • Example: Balloon full of air being released Force of Gravity • All objects in the universe attract each other through gravitational force • Mass increases – force of gravity increases • Distance increases – force of gravity decreases Force of Gravity • Free fall – only force of gravity is affecting an object • Calculate the acceleration at which an object free falls – Earth – 9.8 m/s2 Force of Gravity • Weight is not the same as mass – Depends on gravity – Different locations have different gravities and therefore different weights • Force of gravity on an object is weight – w=mg – Newtons (N)