An electromagnet with 20 turns of wire around an iron nail lifts 5 paper clips. The wire is rewound to 60 turns using the same battery and nail. What most likely happens?

Two balloons rubbed on wool hang on threads 10 cm apart and push slightly apart. The threads are then moved so the balloons hang 3 cm apart. What happens to the push?

A student doubles the current flowing through an electromagnet's coil while keeping the same number of turns and the same iron core. What happens to its magnetic field?

A plastic rod rubbed on cloth 20 times picks up far more bits of paper than the same rod rubbed only twice. What best explains the difference?

Two identical coils carry the same current. One is wound around an iron nail and the other around a wooden pencil. The coil on the nail holds many more paper clips. What accounts for this?

A bar magnet holds a steel paper clip through 2 sheets of paper, but the clip falls when 10 sheets are stacked between them. What is the best explanation?

A student wants evidence that a charged plastic rod acts on water without touching it. Which result would give that evidence?

A student claims a magnet pulls a steel ball without touching it, but her only test pressed the two together. What change would make her test real evidence?

A compass sits 3 cm from a straight wire and touches nothing. Which observation would show that the current in the wire produces a field acting without contact?

A ball is released in midair with nothing touching it, and it speeds up steadily as it falls to the floor. What does this observation show?

A bowling ball and a tennis ball are released together from the same height and reach the ground at the same moment. What does this show?

A space probe travels outward until its distance from Earth is double what it was. What happens to Earth's gravitational pull on the probe?

An astronaut stands on a scale on the Moon and the reading is about one sixth of her reading on Earth, though her body is unchanged. What best explains the smaller reading?

Earth's gravity pulls a falling apple toward the ground. What does the apple do to Earth at that same moment?

The table gives each planet's mass and the reading from the same probe's weight scale resting on its surface. Which claim does the data support?

The Moon circles Earth across about 384,000 km of empty space. What keeps the Moon on that path?

Two magnets with like poles facing are pushed from 10 cm apart to 2 cm apart and clamped there. What happened to the energy stored between them?

A girl lifts a heavy book from the floor and places it on a high shelf. What happens to the energy stored in the book-and-Earth system?

A student pulls two attracting magnets apart and clamps them 8 cm apart. She claims the system now stores more energy than before. Which reasoning supports her claim?

A ball is released from 2 m above the ground and speeds up all the way down. What happens to the stored energy of the ball-and-Earth system as it falls?