BY: BRIANNA SHIELDS

• 1. How do you calculate total force if the two forces are in opposite directions?
• 2. Which of Newton’s laws of motion explains inertia?
• 3. What happens to an object if two forces are equal but in opposite directions?

• To relate gravity and weight
• To define friction and air resistance and design ways to increase it or decrease it
• To define work
• To describe various simple machines

• Gravity • 1. Force of attraction-pulls things downward
• 2. Objects fall at a rate= 9.8 m/s 2
– acceleration due to gravity

1 sec
2 sec
3 sec
4 sec
5 sec
6 sec
7 sec
After falling for 7 seconds what is the acceleration of the ball?
Speed of a falling object
V = 9.8 x t
(V= a(g) x t )

• Terminal
Velocity
• Object no longer accelerates- it travels at a constant speed

• Law of
Universal
Gravitation
• 1. All objects have gravity
• 2. Massive objects = greater gravity
• 3. Objects close together= more gravitational attraction

Less Gravity
More Gravity
Less Gravity More Gravity

• Weight • 1. Amount of gravity that pulls on an object
– Closer to core = more gravitational pull
• 2. Weight changes with location
• WEBSITE : Your weight on other worlds

• Weight • 3. W= m x 9.8
– Weight= mass x acceleration due to gravity
QuickTime™ and a
TIFF (Uncompressed) decompressor are needed to see this picture.

• What would a 10kg book weigh in newtons?
• W = ma = 10kg x 9.8 m/s^2 = ?
• What would a 50kg person weigh in newtons?
• W = ma= 50kg x 9.8 m/s^’2 = ?

QuickTime™ and a
TIFF (Uncompressed) decompressor are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor are needed to see this picture.

Why does the hammer hit the ground before the feather?
• Air resistance
Quick Time™ a nd a
TIFF ( Unco mpre ssed ) dec ompr esso r ar e nee ded to see this pictur e.
• Prevents objects from falling at 9.8 m/s
• Slows objects down
• Object rubs against air molecules
• Pushes upward on objects
• Due to object’s shape

If a feather and a hammer are dropped at the same time on the moon, which will hit the ground first?
QuickTime™ and a
TIFF (Uncompressed) decompressor are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor are needed to see this picture.
Find out by watching “Brain Bytes” NASA Vodcast

• Friction • 1. Exists Where 2 surfaces touch
• 2. Acts in direction opposite to object’s motion

• Often, picking up a heavy object is actually easier than trying to slide it across the floor
Pushing
FRICTION

• Types of friction
• 1. Sliding- produced when solid objects slide over each other
• 2. Rolling Friction- produced by wheels
• 3. Fluid friction- created when an object moves through/across a fluid (water, oil or air)

• Come up with atleast two examples of each friction: sliding, rolling and fluid
• Come up with atleast two examples during which friction would be helpful

• The movement of lubricated engine parts

Compare these two animations. How can the differences be explained?

No Gravity: What will happen when the banana is shot from the cannon?

With Gravity: What will happen when the banana is shot from the cannon?

You will view a photograph of two balls being released from an apparatus.
Which will hit the ground first? The one dropped straight down or the one shot out sideways?
Website: http://www.fearofphysics.com/XYInd ep/xyindep.html

Projectile Motion Tutorial Online: http://www.mhhe.com/physsci/physic al/giambattista/proj/projectile.html

• Work • A force acting through a distance to move an object
– Must be moved over a distance
– Object must move in direction of force
• Work = force x distance

• Work • Examples
– Pushing a desk
– Throwing a baseball
– Lifting a shovel
• Not Examples
– Carrying a grocery bag
– Pushing on a wall
– Carrying a shovelful of snow

• Picking up a grocery bag
• Carrying a grocery bag to the door
• Throwing a baseball 20 meters
• Lifting a suitcase to put into the overhead luggage compartment
• Pushing against a cement slab until exhausted

• Carrying a bag of cat litter home from the store
• Slamming a tennis ball across the net
• Studying all night for the science test
• Finger pushing down the RETURN key on a computer

• Carrying a shovel full of snow from the driveway to the lawn
• You and a friend pushing a heavy piano across a wooden floor
• Standing for half and hour in the freezing cold waiting for the bus to come

• If you lifted an object weighing 200 N through a distance of 0.5 m, how much work would you do?
• W = F x D = 200N x 0.5m = 100nm

• If you picked up a rock weighing 350 N for a distance of 1.0m, how much work would you do?
• W = F x D = 350N x 1.0m = 210 nm

• What do machines do?
• Change small forces into large forces
• Allow small forces to move large objects
• Change the size and direction of the force
• Doesn’t reduce work- divides it into smaller jobs

• Inclined plane
• Ramp, slanted surface
• Ex: truck ramp

• Wedge
• Moving inclined plane with edges
• Ex: knife, scissors, key

• Screw
• Bar wrapped with threads for fastening
• Ex:
– Lightbulb
– Jar Lid

• Lever
• Bar that pivots up and down
• Ex: hammer, teeter toter

• Pulley
• Rope wrapped around a wheel
• Ex: window shade pull

• Wheel and axle
• 2 different sized spinning circles
• Ex: fan, sawblade, screwdriver

• Work with your group members to create your own examples (atleast two) for each machine:
– Pulley
– Lever
– Wedge
– Screw
– Inclined plane
– Wheel and axle

• Site 1: Edheads - Simple Machines
Activities - Lever ...
• Site 2: Simple Machines Made Simpler - by
The Spice B...

• Write the following assignment into your agenda:
– Physics Homework