Download 2 - Holy Trinity Academy

Unit B 2.0 E.notebook
November 25, 2013
Energy
§ the capacity to do work § It can cause changes in motion, shape, temperature, light
§ It can cause physical or chemical changes
§ Forms include: chemical, nuclear, geothermal, wind, solar, tidal, gravitational, kinetic, thermal, electrical, mechanical
§ All forms of energy can be traced back to the sun. The original form of almost all energy on the earth is the sun. Forms of Energy
• Geothermal‐ heat in the earth produced by the radioactive breakdown of matter
• Tidal‐movements of the ocean produced by gravitational attraction of the moon
• Solar‐light from fusion reaction in the sun
• Wind‐produced by differential light absorption and heating of the earth's surface • Chemical‐the energy stored in chemical bonds (POTENTIAL)
• Electrical‐the energy of moving charges
• Nuclear‐the energy stored in the nucleus of atoms
• Elastic potential energy‐the type of energy stored in a compressed spring, a trampoline or a diving board
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Unit B 2.0 E.notebook
November 25, 2013
Energy conversion Technologies
§ Windmills
§ Hydroelectric dams
§ Gas/coal power stations
§ Gas engine
§ Steam engine
§ Electric motor
§ Solar cells
§ Hydrogen fuel cell
Energy Conversions
§ Several things can happen as a result of energy converting from one form to another
§ Change in motion
§ Change in shape
§ Change in temperature
§ Change in light
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Unit B 2.0 E.notebook
November 25, 2013
Gravitational potential energy
§ The stored energy in an object due to its distance above the surface of the Earth; work against gravity
§ It takes more energy (work) to move an object higher above a surface. Thus the higher an object the more energy it will have and the more work it can do when it falls and collides with something on the way down
§ Ep = gravitational potential energy Ep = m x g x d
§ m=mass (kilograms)
§ g=accelerations due to gravity (9.81 m/s2)
§ d=distance (m)
§ Work can be converted to potential energy and vice versa
§ W = F x d (substitute m x a for force)
§ W = m x a x d = Ep 1. A child with a mass of 25.0kg is at the top of a slide in an amusement park. If the vertical height of the slide is 4.00m, calculate the gravitational potential energy of the child.
2. An 800g bird has 47.0J of gravitational potential energy when it is perched high up in a tree. Calculate the bird's vertical height from the ground.
3. A hanging sign is 3.00m above the ground and has 1.47 x 103 J of gravitational potential energy. Calculate the mass of the sign.
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Unit B 2.0 E.notebook
November 25, 2013
Kinetic energy
§ The energy of motion
§ Is a function of the mass and velocity (speed) of the object
§ Ek = ½ mv2
§ Ek= kinetic energy (Joules) m= mass (kilograms) v= velocity or speed (m/s)
1. Calculate the kinetic energy of an electron with a mass of 9.11 x 10­31 kg moving at a uniform speed of 2.00 x 105 m/s.
2. A small toy moving horizontally at a uniform speed of 2.2 m/s has a kinetic energy of 18J. Calculate the mass of the toy.
3. A baseball with a mass of 300g has a kinetic energy of 304 J. Calculate the speed of the baseball.
4. A moving toy with a mass of 7.4 kg has a kinetic energy of 18 J. Calculate the speed of the toy.
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Unit B 2.0 E.notebook
November 25, 2013
Mechanical energy
§ The energy due to the motion and position of an object
§ Em = Eg + Ek = mgh + 1/2mv2
§ Energy is always conserved in any system therefore in any system potential energy of whatever form gets converted to kinetic energy (and other forms) and vice versa so the total energy always remains the same
The potential energy at the top is always equal to the kinetic energy at the bottom. Ep (top) = Ek (bottom) Roller Coaster Animation
1. A seagull flying horizontally at 8.00 m/s carries a clam with a mass of 300g in its beak. Calculate the total mechanical energy of the clam when the seagull is 30.0m above the ground.
2. A 55.0 kg high­jump athlete leaps into the air in an attempt to clear the bar. At the top of the leap, the athlete has a total mechanical energy of 3.00 x 103 J and is moving at 8.33 m/s. Calculate the gravitational potential energy of the athlete.
3. A contruction worker drops a 2.00 kg hammer from a roof. When the hammer is 50.0m above the ground, it has a total mechanical energy of 1.88 x 103 J. Calculate the kinetic energy of the hammer.
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Unit B 2.0 E.notebook
November 25, 2013
Mechanical Energy ­ Ep (top) = Ek (bottom)
1. A 10.0 kg water balloon is dropped from a height of 12.0m. Calculate the speed of the balloon just before it hits the ground.
2. A 30.0 kg child on a trampoline jumps vertically into the air at an initial speed of 1.60 m/s. Calculate how high the child will rise.
1. A 20.0g dart is fired from a dart gun with a horizontal speed of 4.10 m/s. The total mechanical energy of the dart is 0.481J. Calculate the gravitational potential energy of the dart.
2. A pendulum consists of a 500g metal ball suspended on a 50.0 cm string. The ball is pulled horizontally and up a total vertical distance of 10.0cm. It is then released. At the bottom of the arc, the mechanical energy of the ball was determined to be 0.491J. What was the speed of the ball at the bottom of its arc?
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Unit B 2.0 E.notebook
November 25, 2013
Work done = Elastic Potential Energy = Kinetic Energy = Gravitational Potential Energy (CONSERVATION OF ENERGY!)
ex: It takes 150N of force to stretch a trampoline 50cm. If my little sister weighs 50kg, how high will she bounce?
ex: If I shoot my brother with a slingshot by stretching it back 35cm using 48N of force, how fast will a 0.58kg ball be travelling when it hits him?
Pendulum: work is done to lift the ball. This is then equal to Ep. When the ball is released, it has maximum Ek at its lowest point.
Pendulum
Applet
Lab activity
p. 186-187
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