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Inertia! • Kinematics- Study of motion of objects – How objects move • Dynamics- Study of motion of objects WITH FORCES – Why objects move • Mass- Amount of Matter that an object has – Units: Kilogram (kg) – Symbol: m – 1 kg = 2.2 pounds • Inertia- a property of all matter – Tendency of object to maintain its present state of motion • Newton’s 1st law of motion: • Or Galileo’s law of inertia: • Whichever: – An object at rest will remain at rest, and an object in motion will remain in motionat a constant speed and in a straight line, unless acted upon by an external, unbalanced force • A Force is a push or a pull • A Force is what changes the motion of an object • Direction of the Force matters, so it is a vector quantity – Symbol: F – Units: Newton (N) mass times acceleration •Kg*m/s2 Types of Forces • Gravity :is a force of attraction that exists between any two masses • Friction: force resisting the relative motion of solid surfaces • Applied: a force that is applied to an object by a person or another object. Types of Forces cont… • Tension: force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. • Air resistance: frictional force that acts upon objects as they travel through the air. • Normal: support force exerted upon an object that is in contact with another stable object. • A Free Body Diagram is a picture of the object, with all Forces that are acting on it. • The Forces are drawn outward from the center of the body • They can show you the Direction (and magnitude) of the TOTAL Force • If you can’t draw, then just make a dot! • And draw all the forces on the FU object. • Label them!!! FLeft FRight wt The Total Force • At any one time, an object usually has 2 forces acting on it. Think of the rope in a Tug-Of-War: • More specifically, the center of the rope • If 2 forces are going in opposite directions, then one must be thought of as positive, • and the other as negative. • The acceleration that an object experiences FTot is adirectly proportional to the Total m forcem exerted on1itN 1 kg 1 2 sec • That F acceleration is also Tot m proportional to the mass inversely a of the object is what • A Total Force Fchanges a motion of an object Tot mthe F g m • One of the most common forces we deal with is weightG • It is the Force due to gravity • To put it into terms of Izzy’s 2nd: – The acceleration due to gravity is G directly related to the Force due to Mass and Weight are gravity F mg NOT and inversely related to mass (which is not due to gravity) the same thing!!!! Statics • When all forces on an object Balance m FTot 0 - N a 0 2 sec 1. How many forces are T on the sign? 2. Draw the Free Body Diagram FN Joe’s Crap Shak FG Skydivers: • If Roy jumps out of the plane, neglecting air resistance, he will have only one force on him – Weight! FTot Skydivers: • Only an idiot would jump out of plane without a parachute! • You just have to be completely nuts to jump with a parachute! • Since a parachute depends on air resistance, now we have to consider it! FTot Skydivers: • At first, weight is more than the force from air resistance • After a bit of time, air resistance balances weight – If forces are balanced, velocity is constant – That’s Terminal Velocity! • Then the Parachute opens! FTot Skydivers: • Now you have the same weight, but much different surface area! • Air has more material on which to push • Crazy Roy slows down! FTot Skydivers: • Eventually, Air Resistance doesn’t push as hard • Terminal Velocity occurs again, just not as much as before • Lucky for Crazy Roy, anyway! FTot