Physics / Unit 2: Vectors and Motion in Two Dimensions
2.1 Scalars and Vectors
Notes
A scalar has size (magnitude) only. A vector has magnitude and direction.
| Scalars | Vectors |
|---|---|
| distance, speed, time, mass, energy | displacement, velocity, acceleration, force, momentum |
- Draw a vector as an arrow: its length shows magnitude and it points in the direction.
- Vectors in the same direction add; vectors in opposite directions subtract.
- Example: 3 N right plus 5 N left gives a net force of 2 N left.
Practice
Which quantity is a vector?
Acceleration has a direction; the others are scalars.
Two forces act on a box: 12 N east and 5 N west. What is the net force?
Opposite directions subtract: $12 - 5 = 7 \text{ N}$, in the direction of the larger force.
A student says, "My speed is 15 m/s north." What is wrong?
Adding a direction makes it a velocity.
Ready for more? Take the Unit 2 test.