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Energy, Work & Power? What do you think of when you hear the words:

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Page 1: Energy, Work & Power? What do you think of when you hear the words:

Energy, Work & Power?

What do you think of when

you hear the words:

Page 2: Energy, Work & Power? What do you think of when you hear the words:

EnergyEnergy • Universe is made up of matter and energy.

• Energy is the mover of matter.

• Energy has several forms:

– Kinetic

– Potential

– Electrical

– Heat– etc.

http://tiki.oneworld.net/energy/energy.html

Page 3: Energy, Work & Power? What do you think of when you hear the words:

• Conversions from one form of energy to another continually occur.

• Energy cannot be created or destroyed.

Page 4: Energy, Work & Power? What do you think of when you hear the words:
Page 5: Energy, Work & Power? What do you think of when you hear the words:

Work = Force|| x Distance

In this case, the distance is the magnitude of the displacement.

Only the component of force parallel to the displacement does work

Page 6: Energy, Work & Power? What do you think of when you hear the words:

Work• Force applied in the direction of

motion• Work = Force|| Distance• W = F||d• The unit for work is the Newton-

meter which is also called a Joule.• 1 joule is equal to a force of 1 N exerted

over a distance of 1 m

Page 7: Energy, Work & Power? What do you think of when you hear the words:

x

F

xxdFW

xF

yF

Page 8: Energy, Work & Power? What do you think of when you hear the words:

Work or No Work

Page 9: Energy, Work & Power? What do you think of when you hear the words:

m= 10kg

mg = 100N

In this case, the weight does positive work

d = 2 m

Work = mgd = (100N)(2m)

Work = 200 Nm =200J

m= 10kg

Page 10: Energy, Work & Power? What do you think of when you hear the words:

m= 10kg

mg = 100N

In this case, the weight does negative work

d = 2 m

Work = -mgd = -(100N)(2m)

Work = -200 Nm = -200J

Fa

m= 10kg

mg = 100N

FA

Page 11: Energy, Work & Power? What do you think of when you hear the words:

• measured in watts (W)

• One watt of power is expended when one joule of work is done in one second.

Power

http://www.cartoonstock.com/newscartoons/cartoonists/pto/lowres/pton114l.jpg

Page 12: Energy, Work & Power? What do you think of when you hear the words:

Power

• Power is equal to the amount of work done per unit time.

interval time

donework Power

• The unit for power is the Joule/second which is also called a Watt.

Page 13: Energy, Work & Power? What do you think of when you hear the words:

What is horsepower?

• 1 horsepower = 746 Watts

• A horse exerting 1 horsepower can raise 330 pounds of coal 100 feet in a minute, or 33 pounds of coal 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute.

Page 14: Energy, Work & Power? What do you think of when you hear the words:

• Energy possessed by an object due to its motion or its stored energy of position.

• It can either be potential energy or kinetic energy.

• All forms of energy are measured in joules (J).

• Em = Ek + Ep

Mechanical Energy

Page 15: Energy, Work & Power? What do you think of when you hear the words:

Conservation of Energy• Energy cannot be created nor

destroyed; it may be transformed from one form into another, but the total amount of energy never changes.

• So why worry about conserving energy?

http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

Page 16: Energy, Work & Power? What do you think of when you hear the words:

Conservation of Mechanical Energy

• Ek (before) + Ep (before) = Ek (after) + Ep (after)

– When no other type of energy is present.

• Why does a dropped ball not return to its original elevation?

http://www.science-projects.com/Drop/DropBalls.htm

Page 17: Energy, Work & Power? What do you think of when you hear the words:

Energy Transformation of a Pendulum

http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/energy/pe.html

Page 18: Energy, Work & Power? What do you think of when you hear the words:

Potential Energy• (PE) stored chemical energy or

energy of position.

– An object’s ability (potential) to do work by virtue of its position.

– Types: elastic, gravitational and chemical.

• Examples: – Rubber bands– Springs– Bows– Batteries– Gravity?

Page 19: Energy, Work & Power? What do you think of when you hear the words:

Gravitational Potential Energy

• PE = Weight height

• PE = m g h

• Question:– How much potential energy does a 10kg

mass have relative to the ground if it is 5 meter above the ground?

Page 20: Energy, Work & Power? What do you think of when you hear the words:

Potential Energy

• The same work is done on each block.  What mattersis the final elevation, not thepath followed

http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

Page 21: Energy, Work & Power? What do you think of when you hear the words:

Kinetic Energy• The energy of motion.

• Kinetic Energy = ½ mass velocity2

EEkk = ½ mv² = ½ mv²

Page 22: Energy, Work & Power? What do you think of when you hear the words:

mgh

mg

h

How much work does gravity do on the falling mass?

Work = mgh

PE = mgh

Page 23: Energy, Work & Power? What do you think of when you hear the words:

mgh

mg

h

How much energy does the mass have at the bottom of its fall, just before it hits the ground?

Kinetic energy

PE = mgh

v

Page 24: Energy, Work & Power? What do you think of when you hear the words:

mg

h

v

mg

KE = ½ mv2

PE = mgh

If potential energy at top of path is 100 J, how much kinetic energy does the ball have just before it hits the ground and comes to a stop?

Page 25: Energy, Work & Power? What do you think of when you hear the words:

Object Falling from Rest

http://hyperphysics.phy-astr.gsu.edu/hbase/flobj.html#c2

Page 26: Energy, Work & Power? What do you think of when you hear the words:

Practice:

• Think about standing on your desk…if you jumped off, how fast would you be moving just prior to reaching the floor?

• How much work would you do on the floor? (Refer back to previous slide if needed)

http://school.discoveryeducation.com/clipart/images/in-desk.gif

Page 27: Energy, Work & Power? What do you think of when you hear the words:

More Practice

• Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s.

• If the roller coaster car doubled its

speed, what would be its new kinetic energy?

Page 28: Energy, Work & Power? What do you think of when you hear the words:

Calculate speed at positions B,C and D.

Page 29: Energy, Work & Power? What do you think of when you hear the words:

More Energy Transfer

• High speed winds are used to do work on the blades of a turbine at the so-called wind farm.

• Mech. Energy from the air gives the air particles the ability to apply a force to the blades.

• As the blades spin, their energy is subsequently converted into electrical energy (a non-mechanical form of energy) and supplied to homes and industries in order to run electrical appliances.

Page 30: Energy, Work & Power? What do you think of when you hear the words:

Energy Transfer...

• This diagram shows that the potential energy of the boy is changing as he swings. Explain what is happening, in other words how is the energy changing?

Page 31: Energy, Work & Power? What do you think of when you hear the words:

Work/Energy Relationship• If you want to move something,

you have to do work.

• The work done is equal (ideally) to the change in kinetic energy.– what is ideal? is this actual?

• W = KE

http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

Page 32: Energy, Work & Power? What do you think of when you hear the words:

Work-Energy Relationship

• What happens to your stopping distance when you…

• Double your speed?

• Triple your speed?

http://www.thegrid.co.uk/index_files/Mickel-crash-brands.jpg

Page 33: Energy, Work & Power? What do you think of when you hear the words:

Joule to Joule

http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/energy/cs.html

Page 34: Energy, Work & Power? What do you think of when you hear the words:

Forces in Car Crashes

• http://hyperphysics.phy-astr.gsu.edu/hbase/carcr.html#cc3

Page 35: Energy, Work & Power? What do you think of when you hear the words:

Seatbelt Physics

http://hyperphysics.phy-astr.gsu.edu/hbase/seatb.html#cc1

Page 36: Energy, Work & Power? What do you think of when you hear the words:

• The formula for KE is _____?• Kinetic Energy is dependent upon ___ & ____• If an object’s velocity doubles, its kinetic energy

_____. If velocity triples, it will have _____ times the kinetic energy.

• If mass doubles, kinetic energy _____. If mass triples, kinetic energy _____.

• …so what happens to KE if mass doubles and velocity doubles? What if mass is cut in half and velocity doubles?

Page 37: Energy, Work & Power? What do you think of when you hear the words:

Bungee Jumping

• You wish to bungee jump off of a platform. Assuming that there is no air resistance and the spring constant of the 40 m long bungee cord is 100 N/m. How high should your platform be?

• Determine all the forces acting ON the body. • Draw a free body diagram. • Apply Newton's second law. • Think about elastic potential energy.• Solve.

http://images.google.com/imgres?imgurl=http://www.harriahola.net/photos/photos/20040922010930-benjihyppy_kaivarissa.jpg&imgrefurl=http://www.harriahola.net/photos/photo.php%3Fphotoid%3D597&h=614&w=395&sz=58&hl=en&start=16&tbnid=X_UZpiLl13qwzM:&tbnh=136&tbnw=87&prev=/images%3Fq%3Dman%2Bjumping%26svnum%3D10%26hl%3Den%26lr%3D%26safe%3Dactive
http://images.google.com/imgres?imgurl=http://www.harriahola.net/photos/photos/20040922010930-benjihyppy_kaivarissa.jpg&imgrefurl=http://www.harriahola.net/photos/photo.php%3Fphotoid%3D597&h=614&w=395&sz=58&hl=en&start=16&tbnid=X_UZpiLl13qwzM:&tbnh=136&tbnw=87&prev=/images%3Fq%3Dman%2Bjumping%26svnum%3D10%26hl%3Den%26lr%3D%26safe%3Dactive
Page 38: Energy, Work & Power? What do you think of when you hear the words:

Tennis Ball Bounce

Page 39: Energy, Work & Power? What do you think of when you hear the words:

• Elasticity of an object – tendency of the object to return to its equilibrium

(natural ) shape natural shape when Fnet =0

• Restoring Force – the force required to return object to its

equilibrium shape is called the restoring force – it is always directed opposite to the deformation of the object.

Relative “bounciness” of various types of

balls


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