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Answers to Readers' Questions on Physical Science:

Energy

The following 25 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• I want to learn physics in your country
• Use for fusion energy
• Can object have both kinetic and potential energy?
• Kinetic energy of arrow
• How can we save energy?
• Can't figure out the rules of Einstein
• Difference between PE and KE?
• Confused about the three types of kinetic energy
• Can you store pure energy?
• Can something have energy without having momentum?

Next 10

I want to learn physics in your country

Question

August 7, 2009

i want to learn physic at your country but my parent don't have the money to send to school, please help me..... so as my knomledge will not wallow in pain please help

john - Nigeria

18125

Answer

Ideally, you should try to get the basics of Physics, Mathematics and other sciences in your home country before hoping to come to the US to study. This would give you the opportunity to get a scholarship to a college in the US.

Our online lessons can give you an overview and help with your understanding. There are also free online courses for the famous MIT university. They are probably very difficult. You can download their lessons from:

http://ocw.mit.edu/OcwWeb/Physics/

I hope this gives you a start in your study of Physics.

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Use for fusion energy

Question

October 24, 2008

can we use fusion energy for any purpose?

rizwan - Pakistan

16693

Answer

Fusion energy is the same type of energy that powers the Sun. It is much better that nuclear energy (also called fission energy) because fusion energy is not radioactive.

Scientists have worked for years to control fusion energy, so that we can use it, but they still have not perfected the technique.

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Can object have both kinetic and potential energy?

Question

April 15, 2008

I didn't got that why everything has only one energy. Why not an object has potential and kinectic energy both. Is it possible to have both energy.

- USA

15736

Answer

An object can have both kinetic energy and potential energy at the same time.

A ball flying through the air has kinetic energy due to its motion and potential energy because it is above the ground. Also, a rocket has kinetic energy when it is moving and chemical potential energy of its fuel.

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Kinetic energy of arrow

Question

October 26, 2007

An arrow with a mass of 80g is travelling at 80m/s when it reaches its target. it penetrates the target board a distance of 24cm before stopping.
(a) Calculate the arrow's kinetic energy just before impact.
(b) Calculate the average net force between arrow and target.

biar - USA

14645

Answer

The kinetic energy equals one-half the mass times the velocity squared or
KE = (1/2) * m * v * v. You need to change the 80g to 0.08kg to get an answer in joules.

Thus KE = (1/2) * 0.08 * 80 * 80 joules.

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How can we save energy?

Question

October 6, 2007

I am Anbu from Auroville International Township,Auroville,TamilNadu,India.
Recently I am involved in conducting science exhibition for Primary/Elementary level students,Now I am working on the topic ENERGY.
Could you please give some ideas on How to save energy from our day today activities throuh some possible exhibits.
Thanks in advance

- India

14485

Answer

One area in conservation of energy is where we waste the energy we use. Heating or cooling a room that has the windows open is wasteful. Driving an automobile a short distance instead of walking is wasteful. Keeping lights on in a room when no one is in the room is another example of wasting energy.

Another area is to use energy in an efficient manner. That means that scientists and engineers must improve devices and machines that use energy, so that they require less to operate. For example, improvement in electrical devices have made them more efficient, such that they use less energy.

Best wishes in your exhibition.

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Can't figure out the rules of Einstein

Question

September 19, 2007

hi i'm in 9th grade and my teacher isn't teaching me well enough to figure out the rules of the einstein
can u help me?

David - USA

14413

Answer

Newton came up with the rules or laws of Conservation of Energy and Momentum, as well as several other related rules of motion. Years later, Einstein derived the Theory of Relativity that says those laws change when objects approach the speed of light. He also said that gravity is caused by a curvature in space.

What are the "rules" of Einstein that your teacher is trying to teach?

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Difference between PE and KE?

Question

December 20, 2006

Hi,
I am studying physical science and I am having a disconnect in regards to the differnce between PE and KE.
I also am confused with when PE is zero, and when it is a negative.

Please explain
Thank you
Bess

- USA

12660

Answer

KE is kinetic energy or that from moving objects. PE is potential energy that can be turned into kinetic energy.

If you hold a ball up off the ground, it has potential energy and no kinetic energy, because it is not moving. When you let it go, gravity changes the PE into KE.

If the ball is just laying on the ground, it has no PE with respect to the Earth's gravity. It's PE = 0. It might have some chemical PE, but that is a different situation.

With this definition, I don't see how an object could have negative potential energy, unless it was some situation where it was absorbing energy.

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Confused about the three types of kinetic energy

Question

October 29, 2006

Question: I am confused about the three types of kinetic energy:rotational energy, vibrational energy, and translational energy. Would you mind writing the definitions with examples? Thank you so much.

- China

12262

Answer

Kinetic energy means objects are moving. Now, there are several ways in which a molecule or other object can move.

A spinning top has rotational energy. It also exhibits inertia and angular momentum. Rotational energy is also called angular kinetic energy.

When an object is constrained such that it moves back and forth, such as with a vibrating spring, the energy is called vibrational. Note that the motion could also be in a circle or ellipse. Vibrational energy is really a special case of circular energy.

Translational energy is the common kinetic energy of an object moving in one direction.

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Can you store pure energy?

Question

September 20, 2006

Can you store pure energy?

hanneke - Nicaragua

11970

Answer

Energy is the result of motion of matter or radiation. Potential energy is stored energy. A ball held above the ground has potential energy, because when you let it go, it will start moving rapidly. Uranium has potential energy, because when the atom is split, it gives off radiation and fast moving particles. So both cases of potential energy can be called the storage of energy.

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Can something have energy without having momentum?

Question

March 23, 2006

Can something have energy without having momentum? Can something have mementum without having energy?

- USA

10578

Answer

Kinetic energy is the energy of a moving mass. Thus it would have momentum. But chemical energy or light energy are different forms of energy that do not require motion of a mass.

Momentum and energy go hand-in-hand.

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