When Worlds Collide Virtual Lab

Two buggies start 4.0 m apart and drive toward each other. You will predict where and when they crash, before they move. Then you test it on the virtual floor.

Step 1Find the rule (the equation) for a moving buggy. Step 2Practice a crash on paper, four ways. Step 3Measure how fast YOUR buggy goes. Step 4Test your equation on one buggy. Step 5Predict and test the real crash.

Key word	What it means	Symbol	Unit
position	where the buggy is, measured from the zero line	x	m
clock reading	what the stopwatch says	t	s
starting position	where the buggy is when the clock reads 0	xᵢ	m
velocity	how far it moves each second, + or − for direction	v	m/s
collide	two objects at the same position at the same time	—	—

Your work saves in this browser as you go. Each step has a Check button that marks boxes green or red. At the end, press Copy my lab and paste it into the assignment.

A buggy's position was marked once every second.

Clock reading t (s)	0	1	2	3	4	5
Position x (m)	0.30	0.50	0.70	0.90	1.10	1.30

1a. Look at the table. Fill in the boxes.

The buggy movesm during each second.

When the clock read 0 s, the buggy was atm.

1b. Find the position at 10 s and at 47 s. Follow the example.

Example: at t = 3 s → 0.30 + (0.20)(3) = 0.90 m. Check the table: yes, 0.90 m.

At t = 10 s:+ ()(10) =m

At t = 47 s:+ ()(47) =m

1c. Turn the example into a rule in words. Use the word bank.

position = × +

1d. Now write the same rule with symbols. Use the Symbol column in the key-word table.

x = +

1e. A second buggy starts at 4.0 m and moves toward zero, 0.20 m each second.

Moving toward zero, its position gets

So its velocity is

Its equation: x = ( m/s) t + ( m)

At t = 6 s: x = ()(6) += m

Our class equation. Fill in the meanings.

x = v t + xᵢ

Symbol	It means…	Unit
x
v
t
xᵢ

The problem. Two buggies start 4.0 m apart and drive toward each other. Red goes 0.30 m/s. Blue goes 0.10 m/s. Where and when do they crash?

2a. Set up. Choose, then fill in.

	Starts at (m)	Moves toward	Velocity sign	Velocity number (m/s)
Red car	0
Blue car	4.0

A car moving toward zero has a NEGATIVE velocity.

STOP. Check both velocity signs before you go on.

2b. Method 1: Table.

Each row is 2 seconds later. The first three rows are done. Keep adding 0.6 for red and subtracting 0.2 for blue.

t (s)	Red x (m) add 0.6	Blue x (m) subtract 0.2	Gap = Blue − Red (m)
0	0.0	4.0	4.0
2	0.6	3.8	3.2
4	1.2	3.6	2.4
6
8
10
12

2c. Look for the row where the gap is 0.

They crash at t =s and x =m.

The gap gets smaller bym every 2 seconds.

2d. Method 2: Motion map.

Use your table. Click the Red row to put a red dot at each red position, and the Blue row for each blue position. Click a dot again to remove it. Then choose the direction arrow for each row.

Red arrow Blue arrow

2e. Use the word bank: position, time.

They crash where the dots are at the same at the same .

2f. Method 3: Graph.

Pick a color, then click to plot each point from your table. The points connect in order. Click a point again to remove it.

Start with the t = 0 row: Red is at (0 s, 0 m). Blue is at (0 s, 4.0 m).

2g. Read the crossing point.

The lines cross at t =s and x =m.

2h. Method 4: Equations. Use x = vt + xᵢ and your table from 2a.

Red: x = ( m/s) t + ( m)

Blue: x = ( m/s) t + ( m)

The key idea. When they crash, both cars are at the same place at the same time. So Red x = Blue x. Put the two equations equal and solve.

2i. Solve. Follow the example on the left, one row at a time.

Example problem: Green starts at 0 m going +0.2 m/s. Yellow starts at 3.6 m going −0.1 m/s.

Step	Example, done for you	Your turn
1. Set them equal	0.2t = −0.1t + 3.6	0.30t = ()t + ()
2. Get the t's together (add to both sides)	0.2t + 0.1t = 3.6 0.3t = 3.6	0.30t + ()t = () ()t = ()
3. Divide to find t	t = 3.6 ÷ 0.3 = 12 s	t = () ÷ () = () s
4. Put t into the first equation to find x	x = 0.2 × 12 = 2.4 m	x = 0.30 × () = () m
5. Check with the other equation	x = −0.1 × 12 + 3.6 = 2.4 m ✓	x = −0.10 × () + 4.0 = () m Same?

2j. Fill in what each method told you.

Method	Crash time t (s)	Crash position x (m)
Table
Motion map	—
Graph
Equations

Do all the methods agree?

In class, a Timer calls "NOW" every 2 seconds, a Marker puts tape at the front edge of the buggy, and a Measurer measures each tape from the zero line. Here, the virtual group does the timing and marking. You do the measuring.

Your buggy number

Trial Fast forward

Measure a mark:Read the front edge of the blue tape against the tape measure, to the nearest cm.

3a. Record your data. To change cm to m, divide by 100 (example: 45 cm = 0.45 m).

t (s)	Trial 1 (cm)	Trial 2 (cm)	Average (cm)	Average (m)
0	0	0	0	0
2
4
6
8
10
12

3b. Your Average (m) points are plotted for you.

Drag the two round handles to lay the ruler so the line goes through the middle of your dots. One straight line.

3c. Find the slope (the velocity). Pick two points that are ON YOUR LINE and far apart. The handle readout above gives you two.

Point 1: t₁ =s, x₁ =m

Point 2: t₂ =s, x₂ =m

v = (−) ÷ (−) =m/s

Top of the fraction: x₂ − x₁. Bottom: t₂ − t₁.

3d. Write your buggy's equation.

Where does your line hit the vertical axis?m

Is that number less than 0.1 m?

My equation: x = ( m/s) t + ( m)

4a. Pick a distance between 1 m and 3 m. Predict the time.

Distance:m

time = distance ÷ velocity =÷=s

STOP. Lock your prediction BEFORE you run it.

4b. Time three runs.

The start and finish are taped on the floor. Press GO to set the buggy down and start the stopwatch. Press STOP the moment the front of the buggy crosses the finish tape. That's your job as Timer, so watch closely.

0.00

Run 1 (s)	Run 2 (s)	Run 3 (s)	Average (s)

4c. How close were you?

My prediction was off bys.

Check the reason that fits best:

The buggy slowed down (battery).
The buggy drifted sideways.
The stopwatch started or stopped late.
We measured from the wrong edge of the buggy.

Join your partner group. The two buggies start 4.0 m apart, facing each other. Car A (yours) starts at 0 m. Car B starts at 4.0 m.

5a. Set up. The signs are printed for you. Car B moves toward zero, so its velocity is negative.

	Car number	Starts at (m)	Velocity sign	Speed from Step 3 (m/s)
Car A		0	+
Car B		4.0	−

5b. Write both equations.

Car A: x = () t

Car B: x = (−) t + 4.0

5c. Solve. Same steps as 2i.

Step	Your work
1. Set them equal	()t = −()t + 4.0
2. Get the t's together	()t + ()t = 4.0 ()t = 4.0
3. Divide to find t	t = 4.0 ÷ () = () s
4. Find x with Car A	x = () × () = () m
5. Check with Car B	x = −() × () + 4.0 = () m

5d. Your prediction. Copy it from 5c, then lock it before any buggy moves.

Predicted crash timesPredicted crash positionm

STOP. Lock your prediction before any buggy moves.

5e. Run it.

An X is taped at your predicted position. Press GO to set both buggies down and start the stopwatch. Press STOP the moment the front bumpers meet. Then measure where they met from Car A's start.

0.00

Measure a crash:Read the crash mark, in cm, then change to m.

Run	Crash time (s)	Crash position (m)	Miss: how far from the X (m)
1
2
3
Average

5f. How far off were you, in percent? Use the averages.

Miss ÷ actual position =÷=× 100 =%

W1. Choose, then finish the sentence.

The car with the negative velocity was

because it moved toward…

W2. Why does setting the equations equal find the crash? Finish the sentence.

W3. What was the biggest reason for your miss, and how could you fix it?

W4. Optional challenge: Two buggies start 4.0 m apart, pointed the SAME way, at the SAME speed. When do they crash? How do you know?

Make sure your name and period are filled in at the top, then press Submit to Mr. C. Your teacher gets a PDF of your whole lab, including your raw floor data (every tape mark, stopwatch reading and crash position).

If Submit doesn't work, use Copy my lab and paste it into the assignment instead.

Modeling Physical Science · Unit 2 · When Worlds Collide · Virtual