Force Fields and Magnetism
Two factors control how strongly a magnet attracts a iron nail. One is how far away the nail is. What is the other factor?
The strength/magnitude of the magnetic field (or electric current producing it).
An engineer wants her crane’s electromagnet to lift heavier steel beams without changing the iron core or wire type. What two things could she increase to make it stronger?
Increase the number of wire coils or increase the electric current.
Unlike magnetic forces which can attract or repel, what direction does the force of gravity always act?
Gravity always attracts (pulls objects together).
You are sitting on an airplane flying at 500 mph. To the passenger sitting next to you, you are not moving, but to a farmer on the ground below, you are moving extremely fast. What explains this difference?
Your motion depends on the frame of reference / reference point chosen.
A lawnmower engine applies a constant force to push a bag full of grass clippings. As the bag fills up with heavy grass, what happens to the lawnmower's acceleration if the pushing force stays the same?
The acceleration decreases because mass increased (Newton's 2nd Law).
A student holds two North poles of bar magnets close together and feels them push apart without touching. Is this pushing force a contact or non-contact force?
Non-contact force.
A fan plugs into an electrical wall outlet and starts spinning its blades to cool a room. Is the fan acting as an electric motor or an electric generator?
Electric motor (converts electrical energy into motion).
Saturn is far less dense than Neptune, but Saturn has a much greater mass overall. Which planet exerts a stronger gravitational force on nearby objects?
Saturn (gravitational attraction increases with total mass).
A hurricane is traveling across the ocean at 15 miles per hour heading Northwest. Is "15 mph Northwest" a measurement of speed or velocity, and why?
Velocity, because it includes both speed (15 mph) and direction (Northwest).
You want a toy rocket to launch twice as high and accelerate faster into the air. Based on Newton’s 2nd Law, name two separate changes you could make to the rocket.
Increase the thrust force of the motor or decrease the rocket's mass.
Why can you turn off the magnetic pull of a junkyard crane lifting scrap metal, but you cannot turn off the magnetic pull of a refrigerator magnet?
The junkyard crane uses an electromagnet (temporary, controlled by current), while the refrigerator magnet is a permanent bar magnet.
: A hand-crank flashlight has no batteries inside, but when you turn the handle quickly, the bulb lights up. What device inside uses that mechanical motion to produce electricity?
An electric generator.
Although the Sun has far more mass than Earth, human space stations orbit Earth instead of being pulled straight into the Sun. Why?
Earth is much closer to the space station, so Earth's gravitational pull dominates.
Two students play tug-of-war with a rope. Student A pulls to the left with 30 N of force, and Student B pulls to the right with 30 N of force. What is the net force on the rope, and will the motion change?
The net force is 0 N (forces are balanced), so the motion will not change.
When a skateboarder steps forward off their board onto a sidewalk, the skateboard shoots backward behind them. What are the action and reaction forces in this scenario?
The skateboarder pushes backward on the board with their foot. Reaction: The board pushes the skateboarder forward.
Sphere X has a positive charge of +5 and Sphere Y has a positive charge of +50. Which factor will make their repelling force stronger: doubling their charges or sliding them twice as close together?
Sliding them closer together (distance has a major impact on field strength)
A student winds 30 turns of wire around a wooden plastic pen and hooks it up to a 9V battery, but it fails to pick up any paper clips. What key material should replace the plastic pen to make it work?
An iron core (ferromagnetic core).
If gravity was the only force acting on the International Space Station, it would crash straight down into Earth. What property of motion keeps it moving sideways in orbit instead of falling straight down?
Inertia (forward mechanical velocity/motion balanced with gravity).
A soccer ball rests on the grass. A player kicks it right with 20 N of force while a gust of wind pushes it left with 5 N of force. What is the net force, and in which direction will the ball accelerate?
Net force is 15 N to the right (20 N - 5 N = 15 N). It will accelerate to the right.
A heavy wrestler weighs 250 lbs and stands on a bathroom scale. The scale pushes up against his feet with a force of 250 lbs. Which of Newton’s laws explains why these forces are equal in magnitude and opposite in direction?
Newton's 3rd Law of Motion (Action/Reaction force pairs).
Two magnetic poles are brought near each other and push away from one another. What type of poles are they, and what rule explains this behavior?
They are same/like poles (e.g., North and North or South and South). The rule is that same charges/poles repel, while opposite charges/poles attract.
You build three electromagnets using identical iron nails and batteries. Electromagnet A has 15 coils, Electromagnet B has 35 coils, and Electromagnet C has 50 coils. Which electromagnet will attract the fewest paper clips?
Electromagnet A (fewer coils produce a weaker magnetic field).
An asteroid drifts past Mars. If a second asteroid with triple the mass of the first asteroid drifts past Mars at the exact same distance, how does Mars's gravitational force on the second asteroid compare?
It is 3 times as strong (gravitational attraction increases proportionally with mass).
On a position vs. time graph tracking a runner, the line steeply climbs upward for 10 seconds, flattens horizontally for 5 seconds, and then slopes straight down to zero. Describe what the runner did during those three sections.
The runner moved away from the starting point, stopped moving for 5 seconds, and then ran back toward the starting point.
A moving bowling ball hits a single lightweight plastic pin sitting on a lane. During the collision, how does the force exerted by the bowling ball on the pin compare to the force exerted by the pin on the bowling ball, and which object accelerates more?
The forces exerted on both are equal in strength; the plastic pin accelerates far more because it has significantly less mass/inertia.