OwlSheets Students

Zaps and Sweepers at the Indoor Skate Park

0 / 12

Zaps and Sweepers at the Indoor Skate Park

Ask testable questions about electric and magnetic forces, then use data on humidity, time and distance.

From zaps to testable questions

Read the notes, then answer the questions.

Notes From the Northgate Indoor Skate Park

1The Northgate Indoor Skate Park has ramps with smooth plastic surfaces and metal edges called coping. On dry winter days, skaters who ride the ramps often feel a small zap when they grab the coping or a metal railing. Loose hair stands up, and dust and bits of foam cling to the plastic. On humid summer days, this hardly ever happens. Eighth graders Dashiell Ocampo and Yuki Tremaine skate there every weekend. Yuki's first question was "Why is this place so zappy?" Their science teacher, Ms. Florentyna Agbaje, said a better question names one thing to change and one thing to measure.

2Ms. Agbaje explained that when two different materials rub together, electric charge can move from one to the other. Objects with opposite charges pull on each other, and a charged object can also pull on an uncharged one. Over time, charge slowly leaks off an object into the air. It leaks away much faster when the air holds a lot of water vapor.

3For Test 1, the pair rubbed a strip of leftover ramp plastic 10 times with a cotton T-shirt. They held it 5 cm from a small foil-covered foam ball hanging on a thread, and measured how far the ball swung toward the strip. A bigger swing meant a stronger pull. They measured right after rubbing and again 2, 5 and 10 minutes later, using a fresh strip for each trial. They did the test once on a dry day, with 25% humidity, and once on a humid day, with 75% humidity, in the same room.

4The park also has a problem with dropped hardware. Steel nuts and bolts fall off skateboards, and a skater who rolls over one can crash. Each evening, staff push a magnetic sweeper over the floor. It is a bar of strong magnets inside a plastic case on wheels, and its wheels can be raised or lowered. A release handle lifts the magnets 25 mm higher inside the case so the parts drop into a bin. For Test 2, Dashiell hooked a steel axle nut to a spring scale and measured the pull of the sweeper's magnets at different gaps (Table 2). The nut weighs about 0.05 N.

1.

Which question turns Yuki's first question into a testable question about the strength of an electric force?

A. Does the humidity of the air change how far a charged strip pulls a foil ball?B. Is a winter zap at the skate park more annoying than a summer sunburn?C. Why do skaters like plastic ramps better than wooden ramps?D. What made the park choose metal coping for the edges of its ramps?

2.

Match each observation from the park to the testable question it leads to most directly.

3.

Use paragraph 3. Which variable did the pair keep the same in every trial of Test 1?

A. How far the foil ball swungB. The distance from the strip to the ballC. The time since the strip was rubbedD. The humidity of the air in the room

Test 1: The charged strip

Use Table 1 and paragraphs 2 and 3.

Table 1. Swing of the foil ball toward the strip (5 cm away)
Minutes after rubbing	Dry day swing (cm)	Humid day swing (cm)
0	2.4	1.2
2	2.2	0.6
5	1.9	0.2
10	1.5	0.1

4.

Right after rubbing, the swing on the dry day was times the swing on the humid day.

5.

Which statement best describes Table 1?

A. The pull on the dry day stayed near 2.4 cm for 10 minutes, while the humid pull faded.B. The pull grew weaker over 10 minutes on the dry day, but it grew stronger on the humid day.C. The pull grew weaker over 10 minutes on both days, and it faded much faster on the humid day.D. The pull faded at a steady pace, by about 0.3 cm per reading, on both days.

6.

The strip, the ball and the distance were the same at every reading. Which explanation of the weaker pull after 10 minutes fits paragraph 2 best?

A. Charge leaked off the strip into the air, and less charge gave a weaker pull.B. The ball took the strip's charge across the gap, so they now push apart.C. The strip cooled down after rubbing, and cool plastic pulls less.D. The foil ball got heavier as it hung there, so it swung less.

7.

Dashiell wants to find out whether the pull of a freshly rubbed strip changes with distance. Which plan would answer his question?

A. Rub strips of ramp plastic and of wood 10 times, and ask skaters which one gives a bigger zap.B. Hold a strip 5 cm from the ball and measure the swing on a dry day and again on a humid day.C. Rub fresh strips 10 times on one day and, right after, measure the swing at 3, 5 and 7 cm.D. Rub one strip 10 times and hold it 3 cm away, then rub another 20 times and hold it 7 cm away.

Test 2: The magnetic sweeper

Use Table 2 and paragraph 4.

Table 2. Pull of the sweeper's magnets on a steel nut
Gap (mm)	Pull on nut (N)
5	0.8
10	0.3
15	0.12
20	0.08
30	0.02

8.

The pull with a 5 mm gap is times the pull with a 20 mm gap.

9.

Which statement best describes Table 2?

A. The pull got stronger as the gap grew, since the nut had room to swing.B. The pull got weaker as the gap grew, and it dropped fastest at small gaps.C. The pull dropped by about the same amount for each extra 5 mm of gap.D. The pull stayed near 0.8 N until the gap was more than 15 mm.

10.

The sweeper lifts the nut when its pull is larger than the nut's weight, 0.05 N.

The largest gap in Table 2 at which the sweeper still lifts the nut is mm.

11.

The sweeper rolls with its magnets 5 mm above the floor. Use paragraph 4 and Table 2. Why do the nuts drop when the release handle is pulled?

A. The magnets move closer to the nuts, which makes the pull flip and push them off.B. The handle charges the plastic case, which pushes the steel nuts away.C. The handle turns the magnets off, the way a switch turns off a light.D. The magnets end up about 30 mm from the nuts, where the pull is less than their weight.

12.

Yuki says, "How strong an electric or magnetic force is depends only on the objects themselves. Nothing else matters." Do the tests support her idea? Write a claim, give evidence from both tables, and explain your reasoning. Then write one new testable question about the strength of an electric or magnetic force at the park, naming what you would change and what you would measure.