1. When you hit a nail into a board using a hammer, the head of the nail gets warm, in terms of kinetic energy and thermal energy, describe why you think the nail head gets warm. Provide an additional example to help you.
The molecules vibrate rapidly when hammered making it hot.
Or you could say that friction causes nail become hot.
http://wiki.answers.com/Q/Why_does_the_head_of_a_nail_get_warm_when_you_hammer_it
Some of the kinetic energy of the arm’s motion is transferred to thermal energy. The rest of the energy goes into sound, the motion of the nail pushing into wood, and the heat of the nail and the wood.
http://www.need.org/Science of Energy.pdf
2. Describe the kinetic-potential energy conversions that occur when a basketball bounces.
Sample1:
When you bounce a basketball, before you let go of the ball as long as it is in your hands the ball has potential energy. Once you throw it down, or let it fall by itself, it has kinetic energy! The moment it hits the ground potential energy becomes zero and the ball bounces. When your hands stop it the kinetic energy becomes zero and potential energy becomes maximum the cycle goes on!
Sample 2: When the basketball is in your hand, before it is dropped, it has full potential energy. Once that basketball is released from your hands, the potential energy is going to convert to kinetic energy (energy conversions). Right before the ball hits the ground, it has 100% kinetic energy, but the second the ball hits the ground it has 100% potential energy because it has no motion for the little time it is on the ground. When the basketball is bounced back up, the kinetic energy decreases while the potential energy increases. Then the ball reaches your hand and all of the energy is back to potential. This cycle continues. Do not forget that some of the energy when you bounce the basketball is transferred into sound energy (when the ball hits the ground it creates sound).
Sample 3: It doesn't take much effort to lift a ball off the ground. However, work is being done to the ball as it is being lifted, giving it energy. We call this energy potential energy. When the ball is dropped, the ball begins to move. The potential energy begins to be converted into kinetic energy - the energy of motion. There is obviously a very close association between work and energy. Energy is defined as the ability to do work and both work and energy are measured in Joules. To help understand this concept, scientists have classified energy into two types or states. Potential energy is the energy acquired as work is being done to an object and kinetic energy is the energy released by the object as it is doing work. The amount of work put into an object, its potential energy, must always be equal to the amount of work the object can do, its kinetic energy. For example; the higher the ball is lifted off the ground, the higher it will bounce after hitting the ground. Experience tells us that the ball can never bounce back to its original height. The falling ball looses some of its energy to air friction, to internal forces within the ball, and to friction between the ball and the ground on impact. After impact, the ball and the spot directly under the ball are slightly warmer, as some of the energy is lost as heat.
http://Galileo.phys.Virginia.EDU/education/outreach/8thgradesol/EnergyBall.htm
WEDNESDAY, JANUARY 20, 2010
Week1_Prompt#2
Energy cannot be created or destroyed but can be changed into other forms. Potential energy is the measure of an objects position. Kinetic energy is the measure of an objects movement. When kinetic and potential energy combine they create mechanical energy. There can be energy conversions in a basketball. When a basketball is still it is at its potential energy. The basketball's position is being measured. When a basketball is moving it is at its kinetic energy. The basketball's movement is being measured. This is the energy conversion between potential and kinetic energy.
Citations:
Holt, Rinehart, & Winston. (2008). Integrated Science. Austin, TX: Harcourt Education Company.
Posted by csasalaam
at 6:05 PM
3. A car that brakes suddenly comes to a screeching halt. Is the sound energy produced in this conversion a useful form of energy? Explain your answer.
The sound of a car’s brakes screeching to a halt does produce useful energy. The sound of the brakes screeching tells other drivers that the car is coming and that the car is stopping suddenly. This could be a signal to the other drivers to get out of the way in order to avoid an accident. Although the brakes of a car screeching may seem like an unnecessary sound, the sound produced by the brakes can be productive.
(Ms. Douglas)
4. Imagine that you drop a ball. It bounces a few times and then it stops. Your friend says that the energy that the ball had is gone. Where did it go? Evaluate your friend's statement on energy conservation.
The kinetic energy of the ball is converted into elastic energy through deformation (I assume we are not talking about steel balls). The elastic energy is then released, pushing the ball back up. Some energy is lost in the ball where it will cause heating, and some is probably lost to the floor, depending how elastic the floor is, so the rebound bounce won't reach the same height as the initial height, but total energy must be conserved.
http://wiki.answers.com/Q/What_happens_to_the_energy_of_a_ball_when_it_is_dropped_to_the_floor
5. Trace electrical energy back to the sun.
6. Why do you think heating a full pot of soup on the stove could cause the soup to overflow? When heating a pit on the stove energy is being transferred. The energy from the stove is conducting to the pot and then to the soup. As the soup heats up its particles absorb energy, expand and move around more. Since the pot is full, the movement and the expansion of the particles, or atoms, of the soup cause the soup to go over the top of the pot, since the pot does not expand.
7. During thermal expansion, what happens to the density of a substance?
In general density can be changed by changing either the pressure or the temperature. Increasing the pressure will always increase the density of a material. Increasing the temperature generally decreases the density, but there are notable exceptions to this generalization. For example, the density of water increases between its melting point at 0 °C and 4 °C and similar behavior is observed in silicon at low temperatures.
http://www.statemaster.com/encyclopedia/Density
8. A glass of cold water whose particles had a low average kinetic energy was placed on a table. The average kinetic energy in the cold water increased, while the average kinetic energy of the part of the table under the glass decreased. What do you think happened?
There was an energy conversion between the cold water in the glass and the table. The temperature of the water caused the glass to have a low kinetic energy. The energy/heat from the table transferred to the glass.
9. Many cold packs used for sports injuries are activated by bending the package, causing the substance inside to chemically react. How is heat involved in this process?
Cold Packs
Speaking of refrigeration and coldness, have you ever used one of those "instant cold packs" that looks like a plastic bag filled with liquid. You hit it, shake it up and it gets extremely cold. What's going on here?
The liquid inside the cold pack is water. In the water is another plastic bag or tube containing ammonium-nitrate fertilizer. When you hit the cold pack, it breaks the tube so that the water mixes with the fertilizer. This mixture creates an endothermic reaction -- it absorbs heat. The temperature of the solution falls to about 35 F for 10 to 15 minutes.
http://home.howstuffworks.com/refrigerator7.htm
Instant hot and cold packs are used by athletes to quickly and conveniently treat an injury. They last for about 20 minutes. The packs take advantage of chemicals that either absorb a lot of heat or release a lot of heat when dissolved in water. When a chemical process absorbs a lot of heat it is called endothermic. When heat is released, it is called exothermic.
In cold packs, ammonium nitrate is used because it absorbs a lot of heat when it dissolves in water. The water and ammonium nitrate are in separate compartments in the pack. When the cold pack is needed, the chambers are broken and the ammonium nitrate dissolves in the water, absorbing heat and making the pack as cold as 0C.
In hot packs, calcium chloride or magnesium sulphate are used, along with the water. They release heat when the chambers are broken and the chemical dissolves in the water. A hot pack can reach a temperature of 90C.
http://wiki.answers.com/Q/How_do_cold_packs_work
10. When water evaporates (changes from a liquid to a gas), the air near the water's surface becomes cooler. Why?
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