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

Inertia!! vwwabbit.tripod.com/ interior.html What We See What Really Happens

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 motion- at 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: –Units: Newton (N) mass times acceleration Kg*m/s 2

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 object. Label them!!! FUFU wt F Right F Left

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 is directly proportional to the Total force exerted on it That acceleration is also inversely proportional to the mass of the object A Total Force is what changes the motion of an object

One of the most common forces we deal with is weight It is the Force due to gravity To put it into terms of Izzy’s 2nd: –The acceleration due to gravity is directly related to the Force due to gravity and inversely related to mass (which is not due to gravity) Mass and Weight are NOT the same thing!!!!

Statics When all forces on an object Balance 1.How many forces are on the sign? 2.Draw the Free Body Diagram Joe’s Crap Shak FGFG FNFN T

If Roy jumps out of the plane, neglecting air resistance, he will have only one force on him – Weight! 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! 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!

Skydivers: Now you have the same weight, but much different surface area! Air has more material on which to push Crazy Roy slows down!

Skydivers: Eventually, Air Resistance doesn’t push as hard Terminal Velocity occurs again, just not as much as before Lucky for Crazy Roy, anyway!