Vectors: Adding Motion in Two Directions

Lab Brief #11

🎯 Your mission

Learn the rule. Then catch nature using it.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

Velocities and displacements add head-to-tail, not by simple arithmetic. Swim at 2 m/s across a river flowing at 1.5 m/s and your resultant speed over the ground is 2.5 m/s, from Pythagoras, directed downstream of where you aimed.

Key words

vector
A quantity with both size and direction, such as velocity or force.
resultant
The single vector that has the same effect as two or more combined.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Step 1 of 4 · Read

Think about what you just learned: say what "vector" and "resultant" mean in your own words before you start.

Step 2 of 4 · Do

On graph paper, draw a 6 cm arrow east and a 8 cm arrow north head-to-tail. Measure the resultant with a ruler and protractor, then check it against Pythagoras and the tangent ratio. Repeat for two vectors that are not at right angles.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

A swimmer heads across a river at 2 m/s; the current is 1.5 m/s. The resultant speed is:

How sure are you?😐 maybe

Question 2 of 2

Two vectors are added by:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

Next: Terminal Velocity All lessons

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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