Good Morning!

Today we will: launch pennies into the air takes some notes

Please do before the tardy bell: get your lab notebook get out your notes from this week get out something to write with

Warm-Up

Using the formula for the coefficient of friction, solve this problem. Put your work in your notes from this week.

Calculate the μ for wood sliding across carpet if the weight of the wood is 36N and the pulling force is 24N.

You have 2 minutes

Warm-Up II

Calculate the force of sliding friction for a 500 N person using a shoe with a μ of 0.4 Hint: use μ = Ff/FN

Calculate the acceleration of the 500 N person (mass = 50 kg) due to the force of sliding friction. (Hint: use F = ma)

You have 6 minutes to complete

On back of quiz/warm-up

You are a scientist working for ACME Company and your boss asks you to produce data to answer the following question:

What is the effect of velocity on the coefficient of friction between wood and carpet?

Write a hypothesis.

Create a procedure and a data table for the lab you would conduct to test your hypothesis.

What Do You See?

Launching Pennies

Hold down one end of the track or wooden ruler on the table and press down on the other end. Try to get the penny to travel close to the height of the ceiling without hitting the ceiling.

What factors (variables) about the track and how it is positioned determine the height the stone achieves?

You have 8 minutes

Launching Pennies

What is the effect on a penny when additional force (increased deflection) is applied to the ruler?

your hypothesis the data you will record tools you will need to make your measurements

You have 8 minutes

Launching Pennies

Perform your experiment

You have 10 minutes

Law of Conservation of Energy

Law of Conservation of Energy

When a net force acts on an object, what happens? either the speed or position of the object (or

both) change – in other words, the object accelerates

Think about throwing a ball vertically into the air. Draw a sketch of what the ball’s path would look like.

Law of Conservation of Energy

The moment the ball leaves your hand, it has all of the vertical speed it will have – as the ball rises into the air, what happens to its vertical speed?

the vertical speed of the ball decreases

Law of Conservation of Energy

At some point, the ball will reach its maximum height. At this point, the ball’s vertical velocity is zero.

You know what happens next, but do you know what speed the ball will be when it reaches your hand again? when the ball reaches it’s launch height, it will be

traveling at exactly the same speed as it was when it left your hand.

Law of Conservation of Energy

If the speed when you launch the ball is exactly the same as when the ball returns back to the same point, then something is conserved.

What do you think is conserved? seriously – you better be able to figure out the

answer

Law of Conservation of Energy

The Law of Conservation of Energy is pretty simple:

Energy can be neither created nor destroyed; it can only be transformed from one form to another. The total amount of energy remains constant.

Forms of Energy

Energy comes in various forms.

Today, we will be talking about three of them: kinetic energy gravitational potential energy elastic potential energy

Vocabulary Alert!!

kinetic energy is the energy of motion

gravitational potential energy is the energy of position

elastic potential energy is the energy of a spring due to compression or stretch

End Day 1 Notes

Day 2 Notes

Good Afternoon!

Today we will: finish taking notes on the conservation of energy diagram, label, and describe energy transformations use formulas to solve word problems

Please do BEFORE THE TARDY BELL get out your spiral/notes and look over the definitions

for KE, GPE, and EPE pick up the “sample problems” worksheet by the door Pick up a whiteboard and a marker

Kinetic + Potential Energy = Total Energy

In any system – whether it’s the ball you throw vertically in the air or the penny you launched with the ruler, the total kinetic energy + the total potential energy = the total energy in a system

KE + PE = total energy

Our friend Wil E Coyote

Kinetic + Potential Energy = Total Energy

Fun with bowling balls

Do you trust physics?

And now for a song you’ll never get out of your head:

Ole!

Concept Check

Think about the lab we did on Monday when we launched pennies into the air.

elastic potential energy (EPE) gravitational potential energy (GPE) kinetic energy (KE)

were all involved in the energy transformations.

Concept Check

On the back of the sample problems handout, sketch the lab we did Monday: Label the maximum elastic potential energy, the

maximum gravitational potential energy, and the maximum kinetic energy

Below the sketch, describe the entire path of the penny in terms of EPE, KE, and GPE and their energy transformations

You have 12 minutes

Concept Check II

True or False: If you know the maximum kinetic energy in a system, you know the maximum potential energy as well.

TRUE

That was a lot of work! Or was it?

Johnnie pushes against a wall until his muscles tremble.

Carol Anne picks up her pencil.

Who worked harder?

Work

To a scientist, the word work has a very specific meaning.

Work is defined as a force applied to an object over a distance.

Work = force x distance

Work

So, back to Johnnie and Carol Ann.

Who did more work – Johnnie pushing against a wall with all of his might or Carol Ann picking up her pencil?

Let’s “work” a couple of problems

UNIT WARNING!

Before we go much further, we need to emphasize WHAT a Newton is

A Newton is a unit of force that is equal to: 1 kg•m/s2

So BEFORE you start ANY word problem dealing with work or energy, convert your units to kilograms, meters, and seconds!

Formula for Gravitational Potential Energy

The formula for gravitational potential energy is

GPE = mgh

m = mass (kg), g = gravity (m/s2),

h = height (m)

Gravitational Potential Energy

GPE = mgh

Work = fd

How are these two quantities related? mass x gravity = weight (a type of force) height = a type of distance

What ever GPE an object has, it has it because your did that much WORK on it.

GPE = Work Done

Units

If we solve a gravitational potential energy problem AND carry our units all the way through

LIKE YOU SHOULD ALWAYS DO,

you end up with a Newton-meter.

GPE = (mass)(gravity)(distance)

(kg)(m/s2)(m)

Nm

Solve sample problem #3 in your handout

Formula for Kinetic Energy

The formula to calculate kinetic energy is

KE = 0.5mv2

where m = mass (kg) and v = velocity (m/s)

Kinetic Energy

KE = 0.5mv2

looking at the formula, which quantity has the largest influence on the amount of kinetic energy – mass or velocity? Velocity

Units

If we solve a kinetic energy problem AND carry our units all the way through

LIKE YOU SHOULD ALWAYS DO,

you end up with a Newton-meter.

(kg)(m/s)(m/s) = kgm/s2 x m

Nm

Solve sample problem #4 in your handout

Elastic Potential Energy

The formula for elastic potential energy is

EPE = 0.5kx2

k = the spring constant (N/m)

x = amount of bending in meters

the spring constant has to be given – it’s different for different objects

Units

If we solve an elastic potential energy problem AND carry our units all the way through LIKE YOU SHOULD ALWAYS DO, you end up with something called a Newton-meter.

EPE = 0.5 (k)(x2)

N/m m2

Nm

You guessed it - time to work some sample problems!

Newton-Meters

Energy is measured in Newton-meters

Usually, you’ll see it reported as something else, though:

A Newton-meter is called a Joule (J)

Show How Much You Know

The spring constant for the track we used in this lab is 280 N/m

A penny minted after 1982 has a mass of 2.5 grams (o.0025 kg)

If you deflect the track 0.03 m (3 cm) what will be the coin’s maximum velocity how high in the air will it travel how long will it stay in the air

no air resistance, penny travels at a 90° angle to the track, you catch the penny when it returns to the track