You were kidnapped and knocked out. Some time later, you wake up in a dark warehouse. All there is in the room is a scale and a light, so you decide to weigh yourself. WOW!!! You gained a whole lot of weight last night…what happened?

You remember seeing alien figures in a dream-state, and realize you must be on another planet. Is the planet smaller or more massive than Earth?

WARMUP SEPT 17TH - THINK

WEIGHT AND MASS…

Fg = mg (formula for weight)

Fg (weight)is the force an object has due to gravity Gravity on the Earth 9.8m/s2

WEIGHT AND MASS…

What’s the mass of my 893N ex-husband that just happens to be in my basement?

WEIGHT PROBLEMS! FG=MG

What does a 60kg tool weigh?

What’s the mass of a crate of tools that weighs 234 N?

WEIGHT AND MASS:

What does a case of the new Chipotle Gatorade with a mass of 54.8kg weigh?

WHAT WOULD A 60KG TOOL WEIGH:

On Mars (accel of gravity 3.7m/s2 )?

On Jupiter (accel of gravity 24.8m/s2 )?

WHAT PLANET ARE YOU ON?

YOU HAVE A 4KG CAT THAT WEIGHS 14.4N

PlanetGravity : (m/s2)a=

Mercury 3.61Venus 8.83Earth 9.8Earth's Moon 1.6Mars 3.75Jupiter 26Jupiter's Moon Io

1.81

Saturn 11.2Uranus 10.5Neptune 13.3Pluto 0.61

NOW IT’S TIME FOR NEWTON’S 2ND LAW

Newton’s 1st: Inertia. At rest, stay at rest; in motion, stay in motion.

Newton’s 2nd: What happens when a force acts on an object?

Acceleration.

Newton’s Second Law:

Force = mass x acceleration

Force equals mass times acceleration.

F=ma

NEWTON’S SECOND LAW:

• The acceleration of an object is directly proportional to the force applied to the object, and inversely proportional to the mass.

• -or – if F then A

if M then A

CALCULATE THE FORCE HOW DO WE?

HOW? LIKE THIS: My 4 kg cat, Jeter, ran at our kitten Shadow with an acceleration of 3.0 m/s2. He didn’t

stop. Poor little kitten! After suffering a mild concussion, we wondered….how much force did Jeter hit him with?

Force = mass x acceleration, or…

4 x 3 = 12

12 WHAT?

Remember Force has its own special unit…

1kg x 1m/s2 = 1 newton (1N)

F = ma

Learn it. Live it. Love it.

FORCE = MASS(ACCELERATION)

1. How much force is needed to push a lawnmower of 30 kg at 2.5 m/s2?

2. How much force must be applied to a bowling ball that has a mass of 5kg to achieve an acceleration of 25m/s2?

3. What is the mass of a baseball that has an acceleration of 125 m/s2 after a force of 44 Newtons has hit it?

4. What is the acceleration of a 22kg wolf that hits attacks a bear with a force of 400 Newtons?

NOW YOU PRACTICE!

WITHOUT FRICTION…

Friction - a force that opposes motion, or “pushes back” when two surfaces are touching.

It’s always around and it affects everything.

WITHOUT FRICTION…

FRICTION- WORKS AGAINST YOU …..BUT IT CAN BE HELPFUL! WHEN DO I WANT…

A lot of friction? http://www.youtube.com/watch?v=yTKwS-J7qVE

A little bit of friction?

http://digg.com/video/the-science-of-figure-skating http://www.nbclearn.com/olympics

FRICTION TYPES AND PARTS…

There are three Basic Types of Friction

StaticKineticFluid

TYPES OF FRICTION:

1) Static friction: Friction that resists the start of sliding motion between two objects at rest.

Keeps things stopped

TYPES OF FRICTION:

2) Kinetic friction: The force that opposes the movement of two surfaces that are in contact and moving over each other.

To make something move, you just overcome static friction by pulling with a force larger than kinetic friction.

KINETIC FRICTION:

Sliding or Rolling

TYPES OF FRICTION:

3) Fluid friction: The friction between layers of a fluid.

2 types- Liquid and Gas Liquid- water, oil etc.Gas - Air

TYPES OF FRICTION: Described by viscosity.

Viscosity – the “thickness” of a fluid. Low viscosity = “thin;” High viscosity = “thick” or “viscous.”The less viscous a fluid is, the

easier it moves.

Friction DOES depend upon:

1. surface area in contact

2. mass/gravity (weight) of object

3. the texture of the surface

FRICTION IS CUMULATIVE

Small amounts of friction in a system add up to become a large amount of friction.

TEXTBOOK FRICTION…CHALLENGE