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## PowerPoint Slideshow about 'Motion, Forces, & Machines' - tatiana-blackwell

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Describing Motion

- Motion: the state in which one object’s distance from another is changing.
- Are You Moving?
- Reference Point: place or object used for comparison to determine if something’s in motion
- Good Stationary RPs: Trees, Signs, Buildings
- The Backwards Moving Bus
- An Object Is In Motion If It Changes Position Relative To A Reference Point

Relative Motion

- Wait… Are you sure you aren’t moving?
- Movement Depends on your Reference Point
- Chair- NO SUN- YES
- We are actually moving at 30 k/sec

System of Measurement

- Really Important Experiment…. but different units
- It’s important scientists can communicate together
- They must have a “universal language”
- Metric System- International System of Units or S.I
- Base 10
- Length (meter)
- 1 meter = 39.4 inchesor .91 yards
- Centimeters (cm) are used to measures distances less than 1 meter
- 100 centimeters in 1 meter

Easy Conversions!

- Kicking (Kilo)
- Her (Hecto)
- Down (Deka)
- May (meter, gram, liter)
- Damage (Deci)
- Carol’s (Centi)
- Mind (Milli)
- UP to the LEFT, DOWN to the RIGHT

Calculating Speed

- If you know the distance an object travels in a certain amount of time, you can calculate the speed
- Speed = Distance

Time

- Speed: distance object travels per unit of time
- Various ways to express speed: m/s or km/h
- Average Speed: total distance & total time
- Instantaneous Speed: rate at which an object is moving at a given instant time

Velocity & Graphing Motion

- A storm is coming at a speed of 25 km/h!!!
- Velocity: Speed AND Direction of an object’s motion
- What if you want to show somebody motion?
- Line Graph: plotting distance (y) vs. time (x)
- Slope: steepness of the line
- Slope = Rise / Run
- Rise: vertical difference between two points
- Run: horizontal difference between two points

Motion of Earth’s Plates

- Plates: major pieces of Earth’s rocky outer layer
- Fit together like puzzle pieces- Pangaea
- Theory of Plate Tectonics: Earth’s landmasses have changed position over time because they are part of plates that are moving slowly
- Why they movin’?
- Heat from below the Earth pushes rock up
- The cooler rock gets pushed aside and sinks down
- Slow moving action of rock causes plate movement

Plate Movement

- OMG! The Plates are gonna collide!
- Plates move at a rate of only a few mm-cm each year
- Distance = Speed X Time
- Distance = 5 cm / year X 1,000 yrs = 5,000 cm

Acceleration

- The Crazy Life of a Baseball
- Acceleration = Speeding Up….. NOT!!!
- Acceleration: rate at which velocity changes
- Increase speed, decrease speed, change direction- examples??
- Can an object at a constant speed accelerate?
- Yes!! changing lanes, running a curve, ferris wheel

Calculating Acceleration

- Acceleration = Final Speed – Initial Speed

Time

- Units: meters/sec per second m/s2
- Let’s Practice!
- The Black Eyed Peas private plane is about to take off. It reaches a final speed on the runway of 40 m/s after 5 seconds. What is the acceleration of the plane?

Graphing Acceleration

What can we tell from this graph?

Curve= a

Each second traveled a greater distance & speed than the second before

Speed Increasing

Forces

- Force: a push or pull described by its strength and direction
- Newton (N): SI Unit used for measuring the strength of a force
- Exert about 1 N when lifting up a lemon
- We represent forces using arrows
- Arrows point in the direction of the force
- Length of arrow tells strength- Longer = Bigger F

Combining Forces

- Net Force: combination of all forces acting on an object
- Determines if an object moves
- Determines which direction an object moves

5 N

5 N

=

10 N

5 N

10 N

5 N

=

5 N

5 N

=

0

Unbalanced & Balanced Forces

- UnbalancedForce: a net force acting on an object causing it to start or stopmoving or change direction
- Causes a change in the object’s motion
- Balanced Forces: equal forces acting on one object in opposite directions
- Causes no change in the object’s motion

Unbalanced

Unbalanced

Balanced

5 N

5 N

5 N

5 N

=

10 N

5 N

10 N

10 N

10 N

10 N

=

5 N

5 N

5 N

5 N

5 N

5 N

5 N

5 N

5 N

5 N

5 N

5 N

=

=

=

=

0

0

0

0

Friction

- Friction: force that 2 objects exert on each other when they rub together
- Strength of the force of friction depends on:
- 1.) How hard the surfaces push together
- 2.) The types of surfaces involved
- Let’s try it! Rub your hands together
- Friction always acts in the opposite direction to the direction of the objects motion
- Metal Slides… Yikes!
- Without friction, moving objects might not stop until it hits another object

Types of Friction

- Static: acts on objects that aren’t moving
- requires extra force to start motion of objects at rest
- Moving a Desk & Body Builders moving cars
- Sliding: two solid surfaces slide over each other
- Sand on ice, chalk on hands, brakes of bike

Types of Friction

- Rolling: objects roll across a surface
- Easier to overcome than sliding friction
- Skateboards & Bikes use ball bearings
- Fluid: solid objects move through a fluid
- Easier to overcome than sliding friction
- Use of water, oil, or air
- WD40 (oil), streamlined helmet (air), hairy legs (Water) eek!

Gravity

- Gravity: force that pulls objects toward each other
- Issac Newton- Law of Universal Gravitation
- Gravity acts everywhere in the universe!
- A force acts to pull objects straight down toward the center of Earth
- The Famous Apple!

Factors of Gravity, Weight, & Mass

- 2 Things Affect Gravitational Attraction
- Mass- amount of matter in an object (gram)
- More mass = Great Gravitational Force
- Distance
- Farther apart = Less Gravitational Force
- Mass & Weight are NOT the SAME
- Weight- measure of gravitational force exerted
- Force of gravity on person/object at surface of a planet
- Weight varies w/ strength of gravities force, mass doesn’t

Gravity & Motion

- Free Fall: motion of a falling object when the only force acting on it is gravity
- Force of gravity is unbalanced
- Objects in free fall are accelerating
- Acceleration due to gravity on Earth = 9.8 m/s2
- All objects in free fall accelerate at the same rate regardless of mass

Gravity & Motion

- Air Resistance: fluid friction experienced by objects falling through the air
- Upward force exerted on all falling objects in air
- Objects with more surface area = more resistance
- Air resistance increases with velocity
- As object speeds up, resistance gets greater & greater
- Eventually force of air resistance & gravity are equal
- Force is balanced, no acceleration, constant velocity
- Terminal Velocity: greatest velocity a falling object reaches when force of air resistance equals weight of object
- An object that is thrown vertically will land at the same time as an object that was dropped

First Law of Motion- Inertia

- An object at rest will remain at rest, and an object moving at a constant velocity will remain moving at a constant velocity unless it is acted upon by an unbalanced (net) force
- Tennis Game- Ball moves until gravity or friction change objects motion
- If an object is not moving, it will not move until a force acts on it
- Clothes on your bedroom floor!

Inertia

- Inertia: tendency of object to resist change in motion
- Greater the mass of object = Greater Inertia =

Greater force needed to change its motion

Second Law of Motion

- Acceleration depends on the object’s mass and on the force acting on the object
- Force = Mass X Acceleration F = M x A
- Unit of Force = Newtons (N)
- Increase Acceleration = Increase Force
- Increase Mass = Decrease Acceleration
- Boo Yah! Practice Problem!
- You are cruzin’ the streets of Mattoon with an acceleration of 20 m/s in your Lamborghini that has a mass of 1250 kg. What is the net force?

Third Law of Motion

- If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction of the first object…. What????
- For every action there is an equal but opposite reaction
- Action Reaction Pairs: Examples…?

Action Reaction Forces Cancel?

- “Ms. Genta, you said before, forces with equal and opposite direction cancel out and cause no movement…??? You must be trippin!”
- Don’t Cancel If Acting on DIFFERENT objects!

Momentum

- Momentum: quantity of motion
- Momentum = Mass x Velocity (kg m/s)
- Momentum of an object is in the same direction as its velocity
- More Momentum = Harder to Stop
- What same velocity, different mass?
- Car & Baseball both moving at 20 m/s
- Law of Conservation of Momentum: in the absence of outside forces, it can be transferred from one object to another, but none is lost

Rocket Motion

- Rockets rise into the air because it expels gases with a downward force, then the gases exert an equal but opposite reaction force on the rocket
- Upward thrust is greater than downward gravity
- Centripetal force: causes an object to move in a circle
- Force on satellites that are accelerating & revolving around Earth
- Satellites in orbit around Earth continuously fall towards Earth, but because Earth is curved they travel around it

What is Work?

- Work: force exerted on an object causing it to move in the same direction as the force
- Pushing a swing, lifting bags up, pulling blinds down
- It is not work unless the object moves!
- Pushing a car, lifting an enormous boulder
- It is not work unless the motion is in the same direction as the force
- Carrying your books to class
- The good news: Homework is not work!!

Calculating Work

- The amount of work you do depends on both the amount of force you exert and the distance the object moves
- Work = force X distance
- Measured in Joules (J)
- Work done to exert a force of 1 Newton/ 1 Meter
- Heavier Object = Greater Work
- Greater Distance = Greater Work
- Let’s Practice!
- An old, precious lady asks you to move her 95 N sewing kit a distance of 12 m. How much work are you going to have to exert?

Power

- If 1 person sprints up the stairs with a box and 1 person creeps up the stairs with the same box, you are doing the same amount of work but….
- Power: the amount of work done on an object in a unit of time
- Power = Work or Power = Force X Distance

Time Time

- Unit of Power: Watts (W) = 1 J/s
- So… more power to sprint up the stairs!
- Mr. Smith exerts a force of 900 N to push a cart of ice cream down to Ms. Genta’s amazing science students! Oh Ya! The cart moves 250 meters in 40 seconds. What is the power of Mr. Smith?

What is a Machine?

- Machine: device that allows work to be easier
- Hands, shovel, wheelbarrow, crane
- Machines make work easier by changing either the force, distance, or direction
- Input Force: force exerted on the machine
- Input force moves machine- input distance
- Output Force: force machine exerts on object
- Machine exerts a force- output distance
- Input Work = Input Force X Input Distance
- Output work is never greater than Input work

Mechanical Advantage

- Mechanical Advantage = Output Force

Input Force

- Mechanical Advantage the number of times a machines increases a force exerted on it
- Increase Force: M.A greater than 1
- You input 10 N on a can opener
- Can opener outputs 30 N on the can
- Mechanical advantage of 3
- Increase Distance : M.A less than 1
- You input 20 N on a stress ball
- Stress ball outputs 10 N on your hand
- Mechanical advantage of 0.5
- Changing Direction: M.A always equal to 1
- Input force is the same as output force

Efficiency of Machines

X 100%

- Efficiency: compares output & input
- Efficiency = Output Work

Input Work

- Friction decreases the efficiency of machines
- Think about old rusty scissors!
- Efficiency of machines, always less than 100%
- Practice Time!
- Your sweet dad asks you to mow the lawn and pulls the worst lookin’ mower out the garage. I mean this thing was made in 1875. Your input is 250,000 J and the work done by the mower is 100,000 J. How efficient is this machine?

Simple Machines: Inclined Plane

- A flat, sloped surface… aka ramp
- Exert input force over a longer distance
- Input force- pushing or pulling object
- Output force- lifting object without inclined plane
- Input far less than output
- Ideal Mechanical Advantage = Length of incline

Height of incline

Simple Machines: Wedge

- Thick at one end, gradually goes to a thin edge
- Literally moving the inclined plane
- Ideal Mechanical Advantage = Length of wedge

Width of wedge

- Longer, thinner the wedge, greater M.A
- Input Force splits into two output forces
- Examples: knife, zipper, axe, sharpener, mouth

Simple Machines: Screws

- Inclined plane wrapped around cylinder -“spiral”
- Threads on a screw act like an incline plane to increase distance over which force is exerted
- Screw exerts an outward force on the wood
- Closer the threads, greater M.A
- Calculating M.A = Length around threads

Length around screw

- Examples: screws, jar lids, light bulb

Simple Machines: Levers

- Bar that is free to pivot or rotate

on a fixed point

- Fixed point that a lever pivots around: Fulcrum
- Three Classes of Levers:
- 1.) 1st Class- always change direction of input force
- Scissors, pliers, seesaws, paint can opener, lifting neck
- 2.) 2nd Class- increase force, no change direction
- Wheelbarrow, doors, nutcrackers, bottle openers, walking
- 3.) 3rd Class- increase distance, no change force
- hockey stick, fishing pole, shovel, baseball bat, flexing

Simple Machines: Wheel & Axle

- Two circular objects fastened together

that rotate around a common axis

- Object with larger radius – Wheel
- Object with smaller radius - Axle
- Greater the ratio between the radius of the wheel and the radius of the axel- Greater M.A
- Mechanical Advantage = Radius of Wheel

Radius of Axel

- Examples: screwdriver, doorknob, fairy boat

Simple Machines: Pulleys

- Grooved wheel with a rope or cable wrapped around it
- Fixed Pulley: attached to a structure
- Top of flagpole
- Moveable Pulley: attached to moving object
- Construction Cranes
- Block & Tackle: combination of fixed & moveable
- Mechanical advantage is equal to the number of sections of rope that supports the object

Compound Machines

- Compound machines: use two or more simple machines
- Handle- Wheel & Axel
- Screw- also part of axel
- Wedge- Peels Skin
- Lever- suction cup

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