What Does "Magnitude" Mean in Physics?
Reading: What Does "Magnitude" Mean in Physics?
What Is a Vector?
In physics, a vector is a quantity that has both magnitude and direction. For example, if you walk 5 meters east, that movement is a vector—it has a length (5 meters) and a direction (east). Common vector quantities include displacement, velocity, acceleration, and force. The magnitude of a vector is simply how large it is—it tells you how much without telling you which way.
Magnitude vs. Direction
Think of the magnitude of a vector as the “size” of the quantity. If Car A moves 10.0 meters to the west, the magnitude of its displacement is 10 meters. If Car B moves 10.0 meters to the east, the magnitude of its displacement is still 10 meters, even though the direction is different. We usually show direction with; compass directions, a plus or minus sign or with a word like “left” or “right.”
Distance and Displacement
Displacement is a vector; distance is a scalar. Distance only tells you how much ground you covered, while displacement tells you how far you are from where you started and in what direction. But here’s something important: when motion is in one straight line and only in one direction, the magnitude of the displacement is equal to the distance traveled.
Speed and Velocity
Just like displacement and distance, velocity is a vector and speed is a scalar. Velocity tells you how fast you're going and in what direction. Speed just tells you how fast. When motion is in a straight line and in one direction, the magnitude of the velocity is equal to the speed.
Why This Matters
Understanding magnitudes helps you solve physics problems more easily. You can use magnitudes when you're only interested in the amount, not the direction. This is especially useful in early physics problems that involve motion along a straight track, road, or hallway.
Copy any of this information that seems important to you into your physical notebook. Then, see if you can answer the questions that follow based only on your understanding. Refer to your notes if you need to.
❓ Additional problems to solve in your notebook
What does the "magnitude" of a vector represent?
A. Its direction B. Its speed
C. Its size D. Its Position
2. True or False - The displacement of an object is always equal to the distance that it has traveled.
3. Distance is a ____________ quantity.
A. Vector B. Scalar
4. Velocity is a ___________ quantity.
A. Vector B. Scalar
5. When an object is moving in one direction, in a straight line, the magnitude of its displacement will be equal to
A. its speed B. its velocity
C. the distance it travels D. three times the distance that it travels
6. When an object is moving in one direction, in a straight line, the magnitude of its velocity will be equal to
A. its speed B. its displacement
C. the distance it travels D. three times the distance that it travels
7. In physics, we sometimes indicate the direction of a vector with
A. compass directions B. + or - signs
C. directional words like, “left” or “right” D. arrows
E. all of the above
8. True or False - The magnitude of Car B's displacement should be described as "10.0 meters to the east."
9. True or False -The magnitude of Car A's displacement should be described as "10.0 meters"
🧮 Answer Key
C - Its size
2. False - Only when the motion is in a straight line, and in one direction.
scalar
vector
C - the distance that it travels.
A - its speed
E - all of the above
False - When reporting the magnitude of a vector quantity, you don’t include direction.
True
