 # Chapter 4 Newton’s First Law of Motion: Inertia. Newton’s First Law - Inertia In Fancy Terms: Every object continues in a state of rest, or of motion.

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Chapter 4 Newton’s First Law of Motion: Inertia

Newton’s First Law - Inertia In Fancy Terms: Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.

In Plain English: Objects in motion tend to stay in motion. Objects at rest tend to stay at rest.

Inertia Definition: the reluctance of any body to change its state of motion

Examples of Inertia Alphabet soup Removing tablecloth with dishes still on the table http://www.youtube.com/watch?v=QbGV6qQcJrw http://www.youtube.com/watch?v=aCqQzrPCcFM&feature=related

So Why Do Things in Motion Stop?

Forces Definition: any push or pull

Friction Definition: the force that acts between materials that touch as they move past each other

- caused by irregularities in the surfaces of objects that are touching

- Even very smooth surfaces have microscopic irregularities that obstruct motion

MASS a measure of inertia measured in kilograms

MASS AND WEIGHT ARE NOT THE SAME THING!!!

Mass: quantity of matter in an object - independent of location

Weight: force of gravity on an object - depends on an object’s location

Mass and Weight are Proportional but NOT Equal a lot of mass = a lot of weight

SI unit of mass – kilogram SI unit of force - Newton

1 kg = 9.8 Newtons (N) weight = mass x gravity w = mg http://www.youtube.com/watch?v=aCqQzrPCcFM

Net Force Definition: combination of all forces acting on an object

The net forces changes an object’s state of motion In the absence of a net force, objects do not change their state of motion

Normal Force Definition: the upward force that balances the weight of an object Also called support force

Other forces: Tension: At equilibrium – Tension = weight

Equilibrium Net force = zero

Chapter 5 Newton’s 2 nd Law

Remember: Acceleration = change in velocity time interval

What causes acceleration? Force

An objects acceleration is directly proportional to the net force Acceleration ~ net force

Mass resists acceleration Acceleration ~ 1/mass (inversely proportional)

Newton’s 2 nd Law: The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object.

In other words : Acceleration = net force/mass a= F/m

Net Force Unit will always be Newtons. 1 N = kg*m/s 2

Free Body Diagram Definition: Diagram showing all the forces acting on an object.

Applying Force Pressure = force per unit of area Measured in pascals (Pa) Pascal = N/m 2

Pressure = Force area of application P = F/A

Pressure is increased when surface area decreases! ex. bed of nails

Falling and Air Resistance Terminal velocity: speed at which acceleration of a falling object is zero because friction balances weight

Free Fall Explained F = F m m

Chapter 6 Newton’s 3 rd Law For every action there is an equal and opposite reaction

All actions occur in pairs

Action: Object A exerts force on Object B Reaction: Object B exerts force on Object A

Newton’s Law of Universal Gravitation Every object is attracts every other object with a force that for any two objects is directly proportional to the mass of each object.

In other words, the greater the masses, the greater the force of attraction between them

F = G m 1 m 2 d where G = 6.67 x 10 -11 Nm 2 /kg 2

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