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Chapter 4: Problem 4

Why does a ceiling fan continue to rotate even after you have switched it off?

Short Answer

Expert verified
A ceiling fan continues to rotate after being switched off due to the principle of inertia. It eventually stops because of frictional forces acting against the motion.

Step by step solution

01

Understand Inertia

Inertia is a principle of physics, defined by Sir Isaac Newton's first law of motion, which states that an object in motion tends to stay in motion with the same speed and in the same direction, unless acted upon by an unbalanced force. This means, if an object is in motion, it will not stop or change direction unless a force makes it do so.
02

Apply the Principle of Inertia to the Ceiling Fan

In the case of a ceiling fan, after the switch is off, the fan continues to rotate because of inertia. The fan blades were in motion and they tend to stay in motion, even after the power supply is stopped. However, it doesn鈥檛 go on forever.
03

Introduce the Concept of Friction

The fan eventually stops due to the friction between the air and fan blades, and the internal friction within the fan motor. These frictional forces oppose the motion of the fan and gradually slow down and eventually stop the fan.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Newton's First Law of Motion
Newton's First Law of Motion is often called the Law of Inertia. This law tells us that an object at rest stays at rest, and an object in motion continues to move at a constant speed and in a straight line, unless acted upon by an unbalanced force. In simpler terms, things don鈥檛 change what they鈥檙e doing unless something forces them to change.
When you turn off a ceiling fan, it doesn鈥檛 stop turning immediately. This is because of inertia. The fan blades have been set in motion and they want to keep moving. This is why they continue to spin even though the power is off.
Without inertia, the fan would simply stop as soon as the power was cut off, but that鈥檚 not what happens due to the principles defined by this law.
Friction
Friction is a force that opposes motion. It acts between surfaces that touch each other. When it comes to a ceiling fan, friction plays an important role in eventually bringing the spinning blades to a halt.
There are two main types of friction acting on the fan:
  • Air Resistance: This is the friction between the fan blades and air particles. As the fan blades move, they push against the air, which pushes back against them. This slows them down over time.
  • Mechanical Friction: This occurs within the fan motor. Parts rubbing against each other create resistance, further working to slow the fan down until it stops.
Even though friction slows down the fan, it is a very gradual process. This is why the fan doesn鈥檛 stop immediately but slowly loses its speed until it stands still.
Motion
Motion refers to the change in position of an object over time. When you switch on a ceiling fan, you give it energy to start moving. The electric power causes the fan's motor to rotate, creating motion in the fan blades.
Once the fan blades are in motion, they will keep going as long as energy is supplied.
When power is cut off, the motion doesn't stop right away due to inertia, as discussed earlier. Instead, the fan continues to move until forces like friction gradually take away its motion energy.
Motion is a fundamental concept that explains how the fan goes from stillness to spinning and back to rest again.

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