Bell Ringer 11/13

• Explain the difference between KINETIC energy and POTENTIAL energy:

•

Also: get out your TEST: ENERGY and MOMENTUM (I passed it out yesterday) or a BLANK PIECE of PAPER

• (We’ll review your waves test – the one I passed back today – tomorrow or at the end if we have time. )

REVIEW GAME for EXTRA CREDIT• I will state the question.• I will call on a student.• If you can give me the correct answer within 10 seconds, I

will add 5 points to your test grade. • If you are incorrect, or can’t answer, I’ll call on the next

person. • We’ll continue until everyone has earned five points, or we

run out of questions. • NO POINTS FOR SHOUTING OUT ANSWERS! – If you do, the

person I call can steal your answer and gets the points!

Newton’s Laws

• Newton's first law of motion is also called the law of ____.

• 1st law: An object at rest stays at rest and an object in motion stays in motion unless acted on by an unbalanced force. This is called the law of inertia.

Newton’s Laws

• According to Newton's second law of motion, F= ??

• 2nd Law: Force = Mass X Acceleration The harder you push, the greater the acceleration, but the more mass an object has, the less it accelerates with the same force.

Newton’s Laws

• The statement "to every action there is an equal and opposite reaction" is ____.

• 3rd Law: For every action force there is an equal and opposite reaction force. When one object pushes on another object, the second object pushes back (with the same force)

ENERGY

• The SI unit for energy is the ____.• Joules (J) • (This was WRITTEN ON THE BOARD during

your test, where we reviewed ALL the units before the test)

• (J = N*m = kg*m2/s2)

Conservation of Energy• According to the law of conservation of energy, the total

amount of energy in the universe ____.• Conservation means “Stays the same” - remains constant.• As energy transformations occur within a system, the total

energy of the system _______.• Total energy NEVER CHANGES• During energy transformations, energy is never _______.• It STAYS THE SAME – you can’t make more, you can’t get rid

of it, all you can do is transform it from one kind to another.

Types of energy• Which of the following devices does not make use of electrical

energy?• Anything that runs on electricity uses electrical energyd. digital camera

- uses electricityc. Toaster

- uses electricityb. Radio

- uses electricitya. Upright piano

- does NOT use electricity – we have a winner!

Types of Energy

• ____ energy is the energy an object has because of its motion.

• All MOVING objects have kinetic energy

• ____ energy is stored energy due to position.

• Stored up energy is potential energy - The object has the potential to do work

Types of Energy• Anything that can fall has stored energy called ____.a. elastic potential energy

- elastic is STRETCHY – this is stored up from being stretchedb. chemical potential energy

- This is stored up in CHEMICAL bonds (like food or fuel)c. kinetic energy

- This is not potential energy, this is energy in use!d. gravitational potential energy

- If it can fall, it’s above the ground, where gravity can pull it down. We have a winner!

Types of energy

• A bus engine transfers chemical potential energy into ____ so that the bus moves.

• What kind of energy does a MOVING bus have?

• KINETIC!

Kinetic Energy

• The kinetic energy of an object increases as its ____ increases.

• K.E. = ½ mv2

• m = mass – if you make m bigger, K.E. gets bigger

• v = velocity – if you make v bigger, K.E. gets bigger

Potential Energy

• At what point on a roller coaster is the gravitational potential energy (GPE) the lowest?

• GPE = mgh• Smallest h (height) = smallest GPE• (Incline = going up)• (Decline = going down)

Potential Energy

• Increasing the speed of an object ____ its potential energy.

• GPE = mgh• SPEED is not in this equation – no effect

Kinetic Energy• What is the approximate kinetic energy from a baseball’s

forward motion, if the baseball is moving at a speed of 50.0 m/s and has a mass of 0.15 kg?

• G: 50.0 m/s = v• 0.15 kg = m• U: K.E. = ?? J• E: K.E. = ½ mv2

• S: K.E. = ½ X 0.15kg X (50.0 m/s)2

• S: K.E. = ½ X 0.15kg X 2500 m2/s2

K.E. = ½ X 375 J K.E. = 187.5 J or 190 J

Kinetic Energy• A car moving at a speed of 20 m/s has a kinetic energy of

200,000 J from that motion. What is the car’s mass?• G: 20 m/s = v• 200,000 J = K.E.• U: m = ?? kg• E: K.E. = ½ mv2

• S: 200,000 J = ½ X ??kg X (20 m/s)2

• S: 200,000 J = ½ X ??kg X 400 m2/s2

200,000 J / 400 m2/s2 = ½ X ??kg 500 kg = ½ X ?? Kg 1000 kg = ?? Kg

Momentum

• A truck driving along a highway road has a large quantity of momentum. If it moves at the same speed but has twice as much mass, its momentum is ________________.

• Momentum = Mass X Velocity• Twice as much mass = twice as much

momentum. It’s momentum is doubled

Momentum

• A 4 kg object has a momentum of 12 kg•m/s. The object's speed is ___ m/s.

• Givens: 4 kg = mass (m) 12 kg•m/s = momentum (p)

• Unknown: speed (v) = ?? m/s• Equation: p = mv• Substitute: 12 kg•m/s = 4 kg X ?? m/s• Solve: 12 kg•m/s / 4 kg = ?? m/s• 3 m/s = speed

MomentumWhat is the total momentum of the two balls BEFORE the

collision?

Ball one:G: 2 m/s = v 1 kg = mU: p = ?? kg*m/s

E: p = mvS: p = 1 kg X 2 m/s

S: p1 = 2 kg*m/s

Ball two:G: 1 m/s = v 1 kg = mU: p = ?? kg*m/s

E: p = mvS: p = 1 kg X 1 m/s

S: p2 = 1 kg*m/s

Total momentum = Momentum of ball one + momentum of ball two

ptotal = p1 + p2

ptotal = 2kg*m/s + 1kg*m/s ptotal = 3 kg*m/s

MomentumWhat is the total momentum of the two balls AFTER the

collision?

The Law of Conservation of Momentum says that total momentum is conserved. This means that the total momentum NEVER CHANGES

ptotal = 3 kg*m/s ptotal = 3 kg*m/s

Momentum• What is the momentum of the second ball AFTER the

collision?

ptotal = 3 kg*m/s ptotal = 3 kg*m/s

Ball two:G: 2 m/s = v 1 kg = mU: p = ?? kg*m/s

E: p = mvS: p = 1 kg X 2 m/s

S: p2 = 2 kg*m/s

• What is the momentum of the first ball AFTER the collision?

ptotal = p1 + p2

3 kg*m/s = p1 + 1 kg*m/s

p1 = 2 kg*m/s

Momentum• What is the velocity of the first ball AFTER the collision?

ptotal = 3 kg*m/s

G: 1 kg = m 1 kg•m/s = pUnknown: speed (v) = ?? m/s

Equation: p = mvSubstitute: 1 kg•m/s = 1 kg X ?? m/s

Solve: 1 kg•m/s / 1 kg = ?? m/s

1 m/s = speed