WORK,FORCE,MOTION Mr. Thousand Gainesville Middle

MOTION Motion is defined as a change in an objects position over time. How can you tell or be sure that motion has occurred? You have to have a reference point.

MOTION ANALYZED When we study motion there are several key factors that you need to know  Reference Point  Speed  Velocity  Acceleration

REFERENCE POINT In order to prove motion you must observe that an object moves in relation to some other object that is not moving. The earth’s surface and objects on it are common reference points.

SPEED The rate of motion is a measurable thing. We call this speed. SPEED: Distance Time Metric Unit: m/s meters per second Kilometers per hour English units: Miles per hour

Average Speed Very few items in motion travel at a constant speed. Average Speed: Total Distance Total time

What is her average speed? If this girl walks the following distance in 6 seconds, what is her average speed?

Average speed problems Susie walks to my house from school. She takes 25 minutes to walk 1.5 Kilometers. What is her average speed? Weronique ( Mrs. T’s horse) is moving around the pasture grazing. She moved 15 meters in 30 s, 25 meters in 30 seconds and 5 meters in 45 s. ( good grass). What is her average speed?

VELOCITY Here is a riddle: Two students skip school and they both travel at 6 Km/h for 15 minutes and then they see Mr. Keenan and travel at 12 Km/h for 5 minutes. One of the students gets caught but not the other? Why not?

VELOCITY In addition to speed, motion also occurs in a specific direction. The speed an object moves in a particular direction is called VELOCITY. Susie is walking at a velocity of 2.2 Km/h north.

Velocity or speed? Jimmy is racing on a the track at 120 Km/h. The birds flew south at 20 m/s. The cattle drive was moving at 4 Km/h west. The dog chased the cat at 3 Km/h. The students walked left down the hall at 6 Km/h.

ACCELERATION Acceleration is defined as the rate at which velocity changes. *Remember that velocity involves speed, direction or both* Positive acceleration: You go faster and maybe change direction Negative acceleration: You go slower and maybe change direction Continuous acceleration: If you go in a circle you are constantly changing direction so velocity changes constantly so you are always accelerating.

ACCELERATION MATH A= Vf –Vi T A= Acceleration V= Velocity f= Final i= Initial T= Time

TRY THIS ONE A car accelerates from a standstill to 60 Km/hr in 10.0 seconds. What is its acceleration? A car accelerates from 55 km/hr to 25 km/hr in 30 seconds. What is its acceleration?

At a track meet at Gainesville Middle School, a runner does one complete 800 meter lap in 1.5 minutes. Assuming she starts and stops at the same point: a. What was her average speed during this lap? b. What sort of acceleration does the runner have?

NEWTON’S LAWS Sir Isaac Newton developed three laws of science that describe the motion of all common objects

1686: “Principia” Newton theorized in this book about motion, what it was, what stopped or started motion and why things resisted stopping or starting at all.

Big ideas behind the Laws! What kinds of things will act upon objects to make them move or stop moving?

FORCE Defined as a PUSH or a PULL

MORE ABOUT FORCE Force is measured in the metric unit: Newton (N). More than one force can be interacting with an object at one time. Forces can be in the same direction or be opposite. Unbalanced force causes motion.

FAMILIAR FORCES GRAVITY FRICTION

Probably the more correct version of the story is that Newton, upon observing an apple fall from a tree, began to think along the following lines: The apple is accelerated, since its velocity changes from zero as it is hanging on the tree and moves toward the ground. Thus, by Newton's 2nd Law there must be a force that acts on the apple to cause this acceleration. Let's call this force "gravity", and the associated acceleration the "acceleration due to gravity". Then imagine the apple tree is twice as high. Again, we expect the apple to be accelerated toward the ground, so this suggests that this force that we call gravity reaches to the top of the tallest apple tree

GRAVITY Gravity is an invisible force of attraction that all objects have. The amount of gravity an object has is directly related to it’s mass.

GRAVITY CONTINUED The more mass an object has the more gravity it exerts Earth has more gravity than the moon because it has much more mass. The distance between two objects also affects how much Gravity pulls each.

MASS vs. WEIGHT Mass is defined as the amount of matter in a set volume. The mass of an object remains constant throughout the universe. Measured with a balance. Weight is a measurement of how gravity affects an object. The more gravity the object is subjected to, the greater it’s weight. Measured with a scale.

Think about it? The gravity of Jupiter is 2.5 times that on earth. How does that affect your weight on Jupiter? Your mass on Jupiter?

FRICTION Friction is a force that opposes motion (works against) when two surfaces are touching each other.

NEWTON’S FIRST LAW: INERTIA An object at rest remains at rest and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.

INERTIA Newton’s 1 st law recognized that the more mass an object has, the more Inertia the object has The more mass, the harder it is to change the speed or acceleration of the object. Which ball the golf or bowling ball has the most inertia?

INERTIA IN SPACE Objects in space travel in straight lines and forever unless they hit something else. Why? How is this an example of Newton’s 1 st Law?

Newton’s 2 nd Law of Motion The acceleration of an object depends on the mass of the object and the amount of force applied.

2nd Law: mathematically Acceleration = Force Mass Force= Mass X acceleration

What is the acceleration of this dog sled?

a.What is the force of an object that has a mass of 25 Kg and is accelerating at a rate of 10 m/s/s? b. How much force is necessary to make an object with a mass of 30 Kg, accelerate at a rate of 25 m/s/s? LET’S TRY SOME

Newton’s 3 rd law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. “For every action there is a equal and opposite reaction”

MOMENTUM Newtons Three laws help describe why objects have momentum. Momentum is the property of a moving objects that describes how the mass and velocity of the object affects how much force is needed to stop or change the direction of the moving object. The more mass or velocity an object has the harder it is to change it’s movement.

WHAT IS WORK? Which of these examples describes the physical science description of work? You throw a bowling ball down the lane and 6 pins fall over. You read a whole chapter of your favorite book. You run through the airport with a heavy backpack. You pick up a heavy rock from the ground.

WORK Work is defined in physics as having occurred when a force causes an object to move in the SAME direction as the force.

CALCULATING WORK Work= F X d Force X distance Metric unit: Joules

WORK PROBLEMS How much work does a horse do when it pulls with a force of 1000N along a path 800 meters long? How much work does a person do when they lift a box with a force of 500 N up onto a table 1.5 meters tall?

objectForce (N) Distance (m) Time (s) Work n X m=J Power J/s= W What work feels like.

POWER Power is defined as the rate at which work is done. P= W t Power is work divided by time The metric unit for Power is: Joules/second more simply called Watts

What is a machine? Machines are devices that are used to make work easier. Machines make work easier by multiplying forces. (Mechanical Advantage) Machines change the size and/or direction of a force. Remember: machines cannot reduce the total force necessary to do a task, but change how the force is applied or used.

Output vs. Input force The input force is the force you apply to the machine. The work done by the machine is output force. Input =output + friction Work output can NEVER be greater than input and is generally less than input due to friction.

Mechanical Advantage and Efficiency Mechanical advantage tells you how many times the machine multiplies the force. MA= output force input force Mechanical efficiency: How well a machine overcomes the force of friction ME= Work output Work input

REDUCE THE FRICTION! The force of friction is a big factor in the amount of force needed to do work. You can make machines more efficient by reducing the amount of friction. How would you do this? 1) Small surface areas 2) Lubricants such as oil or grease

Levers Levers are composed of a bar that pivots on a fixed point called the fulcrum. Levers will change the direction of the force and depending on where the fulcrum is the MA can be more than 1.

PULLEY: 2 Kinds Grooved wheel and rope that runs through the wheel. FIXED: Attached to a non-movable object: Changes direction of input force but does not increase or decrease the amount of force.

Movable Pulley Movable pulley: Attached to the object they are moving. These movable pulleys do NOT change the direction of the force but do multiply the force for additional mechanical advantage.

INCLINE PLANE A ramp! The incline plane creates mechanical advantage by allowing you to move the load over a longer distance.

WEDGE A double inclined plane that moves. Examples: Knife, doorstops, axe heads

SCREWS Incline plane wrapped around a spiral. Most screws are used as fasteners or to hold on lids.