Mechanical Work: Forces, Energy, Power, and Conservative Systems

All flashcards

What is work in physics?

Work is energy transferred to or from an object when a force acts through displacement of its point of application.

What is the constant-force work formula?

For force magnitude $F$, displacement magnitude $s$, and angle $\theta$ between them, $W=Fs\cos\theta$.

When is work positive?

Work is positive when the force has a component in the direction of displacement.

When is work negative?

Work is negative when the force has a component opposite to the displacement, such as gravity acting on a ball thrown upward.

What is one joule?

One joule is the work done by a one-newton force acting through one metre in the direction of the force: $1\,\mathrm{J}=1\,\mathrm{N\,m}$.

Quiz questions

1. For a particle, what does the work–energy principle state?Answer: Net work equals the change in kinetic energy.
2. What characterizes the work done by a conservative force between two points?Answer: It is independent of the path between the points.
3. What is the instantaneous power delivered by a force acting on an object?Answer: $P=\mathbf{F}\cdot\mathbf{v}$
4. For constant torque aligned with a fixed rotation axis, what is the rotational work over angular displacement $\Delta\phi$?Answer: $W=\tau\Delta\phi$
5. Under the convention that work done by a gas is positive, what is the sign of that work during expansion?Answer: Positive, because the gas volume increases.