The rate at which work is done or energy is transferred, measured in watts (joules per second). Power determines how quickly engines, motors, and electrical devices can deliver energy.
Definition
The rate at which work is done or energy is transferred, measured in watts (joules per second).
💡 Intuition
How fast you use or produce energy. A powerful engine does work quickly.
🎯 Core Idea
Power measures how quickly energy is transferred — the same work done faster requires more power.
Example
Formula
Notation
P is power in watts (W), where 1 W = 1 J/s. W is work in joules, t is time in seconds, F is force in newtons, and v is velocity in m/s.
🌟 Why It Matters
Power determines how quickly engines, motors, and electrical devices can deliver energy. It is the key specification for car engines, light bulbs, and power plants, and governs electricity bills and energy efficiency ratings.
💭 Hint When Stuck
When solving a power problem, first determine whether you know work and time or force and velocity. Then use P = W/t if you have work done over a time interval, or P = Fv if you have a constant force and velocity. Finally, check that your units are in watts (joules per second).
Formal View
Related Concepts
See Also
🚧 Common Stuck Point
A small motor can do the same work as a big motor—it just takes longer.
⚠️ Common Mistakes
- Confusing power with energy or work — power is the rate of energy transfer, not the total amount of energy transferred.
- Forgetting to convert units — mixing kilowatts with joules or hours with seconds leads to incorrect answers.
- Using P = Fv when the force is not constant or not in the direction of motion — the general form requires P = \vec{F} \cdot \vec{v}.
Go Deeper
Frequently Asked Questions
What is Power in Physics?
The rate at which work is done or energy is transferred, measured in watts (joules per second).
What is the Power formula?
When do you use Power?
When solving a power problem, first determine whether you know work and time or force and velocity. Then use P = W/t if you have work done over a time interval, or P = Fv if you have a constant force and velocity. Finally, check that your units are in watts (joules per second).
Next Steps
Cross-Subject Connections
How Power Connects to Other Ideas
To understand power, you should first be comfortable with work and energy. Once you have a solid grasp of power, you can move on to electrical power.
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