📚 Topic Summary
In physics, work has a very specific meaning. It's the energy transferred to or from an object by a force causing displacement. For work to be done, a force must act on an object, and that object must move some distance in the direction (or component of the direction) of the force. Remember, if there's no movement, there's no work, even if a force is applied! Work is a scalar quantity, meaning it has magnitude but no direction. The unit of work is the Joule (J), which is equivalent to a Newton-meter (N⋅m).
Mathematically, work ($W$) is often defined as the dot product of the force vector ($\vec{F}$) and the displacement vector ($\vec{d}$):
$W = \vec{F} \cdot \vec{d} = |\vec{F}| |\vec{d}| \cos(\theta)$,
where $\theta$ is the angle between the force and displacement vectors.
🧠 Part A: Vocabulary
Match the term to its definition:
| Term |
Definition |
| 1. Work |
A. The distance an object moves during an interaction. |
| 2. Force |
B. The transfer of energy when a force causes displacement. |
| 3. Displacement |
C. The SI unit of work, equivalent to a Newton-meter. |
| 4. Joule |
D. A vector quantity that causes or tends to cause acceleration of a body |
| 5. Scalar |
E. A quantity, such as mass or volume, that has magnitude but does not have direction |
(Answers: 1-B, 2-D, 3-A, 4-C, 5-E)
✍️ Part B: Fill in the Blanks
Complete the following paragraph using the words: energy, force, displacement, Joules, angle.
Work is the transfer of ___________ when a ___________ causes ___________. The unit of work is ___________, and the amount of work done depends on the ___________ between the force and displacement vectors.
(Answers: energy, force, displacement, Joules, angle)
🤔 Part C: Critical Thinking
Can work be negative? Explain, providing an example.
(Answer: Yes, work can be negative. This happens when the force and displacement are in opposite directions (the angle between them is greater than 90 degrees). For example, if you are slowing down a sliding box by applying a force in the opposite direction of its motion, you are doing negative work on the box.)