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Transcript of Energy
can you name any? Types of Energy Mechanical Energy Nonmechanical Energy Kinetic Energy Potential Energy Chemical Energy Nuclear Energy Electrical Energy Incorporates Kinetic and Potential all in one
Potential energy PLUS kinetic energy is the total amount of mechanical energy Mechanical Energy = KE + PE Special forms of energy Chemical Energy Nuclear Energy Electrical Energy KE = 1/2 m v^2 Kinetic Energy = 1/2 X mass X speed squared elastic potential energy gravitational potential energy PE = mgh Potential Energy = mass X acceleration due to gravity X height In your tree what two things make up mechanical energy? energy released when bonds break and form new bonds Fusion and fission: the change in subatomic particles movement of charged particles (electrons) Which would have larger kinetic energy? Which would have larger kinetic energy? so Kinetic Energy depends on what two things? the unit for KE is Joules (J) Does it take energy to draw this bow?
Is there energy when you let go? So is there energy between the time you draw the bow and the time you release the arrow? Created when an item is stretched or compressed created when two objects are separated by a distance which one had greatest potential energy at the top? which video had the greatest potential energy? Can energy be created?
Can energy be destroyed? WHAT?
the total amount of energy in the universe never changes, it never disappears...
Where does it go?!?
It just changes forms How about when you hit the brakes in your car?
where does the energy go? Kinetic energy and potential energy transform between each other. Mechanical energy can be transferred to other forms (nonmechanical energy). so gravitational potential energy depends on what two things? the unit for PE is Joules (J) practice problems What is the kinetic energy of a 3-kilogram ball that is rolling at 2 meters per second? Missy Diwater, the former platform diver for the Ringling Brother's Circus had a kinetic energy of 15,000 J just prior to hitting the bucket of water. If Missy's mass is 50 kg, what is her speed? You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand with a speed of 30 m/s, what is the kinetic energy? Find the mass of a car that is traveling at a velocity of 60 m/s North. The car has 5,040,000 J of kinetic energy. Practice Problems The potential energy of a 40-kg cannon ball is 14000 J. How high was the cannon ball to have this much potential energy? A 75-kg refrigerator is located on the 70th floor of a skyscraper (300 meters above the ground) What is the potential energy of the refrigerator? The potential energy of an apple is 6.00 joules. The apple is 3.00-meters high. What is the mass of the apple? What potential energy is acquired by a hammer with a mass of 0.75 kg when raised 0.35 m? KE KE PE PE As height increases our potential energy gets bigger.
as height decreases our kinetic energy gets bigger. What about roller coasters? Conservation of Energy Problems Realize that energy never disappears, it must be conserved
Kinetic and potential just switch between each other remember that PE + KE = TME So you know that KE + PE = KE + PE i i f f A .003 kg lump of ice falls from an airplane as it comes in to land. If the ice hits the ground with a vertical speed of 85m/s, what was the height of the plane when the ice fell off?
A. What is your kinetic energy at the time of impact?
B. What is the maximum Potential energy?
C. Solve for height a 2 kg ball is dropped from a height of 6 meters. Initially How much PE does it have?
How much KE does it have? Finally How much PE does it have?
How much KE does it have? So PE + KE = TME So PE + KE = TME i i f f A 500 kg pig is standing at the top of a muddy hill on a rainy day. The hill 30.0 m high. The pig slips and begins to slide down the hill. What is the pig’s speed at the bottom of the hill?
a. find potential energy initial
b. What is kenetic energy final
c. what is speed? so movement (kinetic energy) can be converted to light, sound, waves, heat (nonmechanical/other forms of energy). In order to CONSERVE energy two things happen... Mechanical energy can be converted between itself (kinetic to potential or potential to kinetic). What do I mean???
lets drop a balloon from the top of a building (pic 2) 1 2 initially (pt B) what is initial PE
what is initial KE finally (pt A) what is final PE
what is final KE Lets throw a balloon towards the top of a building (pic 1) finally (pt B) what is final PE
what is final KE Initially (pt A) what is the initial PE
what is the final KE The momentum of an object depends on two things: p = mv momentum = mass X velocity When/where do you hear the word "momentum" being used? The Denver Nuggets have all the "momentum" going into the playoffs...
So what does momentum really mean? In other words an object is "on the move" and is "hard to stop" It is "mass in motion". All objects have mass so if the object is moving then it has momentum How much "stuff" is moving and how "fast" the stuff is moving. Conservation of Momentum In the same way energy is conserved in our universe, momentum is too. Momentum always stays constant, it transfers from one object to another.
The total momentum after a collision is the same as before the collision. Types of collisions Elastic collisions colliding objects "rebound" or bounce off each other quickly Inelastic collisions Demonstrations:
two balls of varying masses
two cars Questions... two balls of EQUAL mass, one is stationary (no speed) and the other is moving.
What will happen to both balls? Why? two balls of UNEQUAL mass, both moving towards each other with the same speed.
What will happen to both balls? Why? two balls of EQUAL mass, both moving towards each other but with different speeds.
What will happen to both balls? Why? very similar to our old friend INERTIA What type of things are elastic?
so what words come to mind when you hear elastic? Stretchy, bouncy, etc... In this type of collision the kinetic energy of the system is conserved.
in other words the total KE (movement) is the same before and after the collision. A perfect elastic collision rarely occurs on earth due to other forces acting on objects and energy dissipating to surrounding objects. Colliding objects "stick" together after contact and do not bounce off In this type of collision the kinetic energy is NOT conserved
in other words some energy is lost to the surroundings What would happen if you have a really big ball moving slowly and a small ball moving really fast? Remember in ALL collisions the momentum IS conserved!