Explaining How a Fridge & Meteorite Work With the First Law of Thermodynamics

[Jason_Hyde]

Hi,
I was woundering if somebody could explain to me using the equation
ΔU = Q + W (The first law of thermodynamics)

• how a fridge works?
• what happens with a meteorite?
• what happens with a standard fan?

Much appreciated
--
Regards
Jason_Hyde

 

[Andrew Mason]

Hi,
I was woundering if somebody could explain to me using the equation
ΔU = Q + W (The first law of thermodynamics)

To be clear: W here is the work done to the system. Q is the heat flow into the system minus the heat flow out of the system.

• how a fridge works?
• what happens with a meteorite?
• what happens with a standard fan?

We aren't going to give you the answer but we can help you find the answer.

The first question is a matter of applying the first law of thermodynamics to a reversed heat engine cycle (which extracts work from heat flowing from a hot to a cold reservoir) to cause heat to flow from a cold to a hot reservoir by adding work to the system.

For the second, think of the kinetic energy of the meteorite doing work on the Earth's atmosphere.

For the third example, think of the fan as doing work on air (a gas) by creating a low pressure on one side and a high pressure on the other.

AM

 

[quicknote]

Sure, I would be happy to explain how a fridge and a meteorite work with the first law of thermodynamics.

The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, but can only be transferred or converted from one form to another. It is represented by the equation ΔU = Q + W, where ΔU is the change in internal energy of a system, Q is the heat supplied to the system, and W is the work done by the system.

Now, let's apply this law to a fridge. A fridge works by transferring heat from inside the fridge to the outside, thereby keeping the inside of the fridge cool. This is possible because of the refrigerant, a substance that absorbs heat when it evaporates and releases heat when it condenses. The compressor in the fridge compresses the refrigerant, causing it to condense and release heat. This heat is then dissipated outside the fridge, while the cool refrigerant is circulated back inside to absorb more heat. In this process, the first law of thermodynamics is at play, as the heat (Q) is transferred from inside the fridge to the outside, while the work (W) is done by the compressor.

Now, let's consider a meteorite. When a meteorite enters Earth's atmosphere, it experiences a significant amount of air resistance, causing it to heat up and eventually disintegrate. This is because the kinetic energy of the meteorite is being converted into heat energy, in accordance with the first law of thermodynamics. As the meteorite travels through the atmosphere, it transfers its kinetic energy to the air molecules, causing them to vibrate and generate heat. This process continues until the meteorite is completely disintegrated, and all its kinetic energy has been converted into heat energy.

Lastly, let's look at a standard fan. A fan works by converting electrical energy into mechanical energy, which is then used to move the blades and create air flow. This conversion of energy is in accordance with the first law of thermodynamics, as the electrical energy (Q) is converted into mechanical energy (W) to do the work of moving the fan blades.

In summary, the first law of thermodynamics plays a crucial role in explaining how a fridge, meteorite, and standard fan work. It governs the transfer and conversion of energy in these systems, allowing us to understand and explain their functioning. I hope this explanation