8th Grade Unit 7 Lessons 1-3

What is the gravitational force acting on an object that has a mass of 10.0 kg?

• 0.2 kg·m/s2

• 9.8 kg·m/s2

• 10.0 kg·m/s2

• 98.0 kg·m/s2

If i set an object on a scale that is 0.500 kg, the weight of an object is given by F = mg, where g = 9.8 m/s2. With what force does the object push down on the balance?

• 0.500 kg·m/s2

• 4.90 kg·m/s2

• 9.3 kg·m/s2

• 9.8 kg·m/s2

Which statement about the universality of gravity is untrue?

• The gravitational force between two objects depends only on their masses.

• The gravitational force between two objects increases if the mass of one object increases.

• The gravitational force between two objects increases if the distance between the objects decreases.

• Any two objects that have mass also have a force of gravity acting between them, no matter how far apart they are.

When Bethany walks across a carpet, her socks pick up many negative electric charges. Later in the day, these negative charges are no longer present on her socks. What most likely happened to the negative charges?

• The charges disappeared.

• The charges transferred to another object.

• The charges switched from negative to positive.

• The charges broke apart into smaller positive and negative particles.

Peter’s teacher tells him that he should not place his electric stereo near the edge of a pool because the water in the pool is a conductor. What does she mean when she says that the water is a conductor?

• Water is a type of electrical energy.

• Water damages electric circuits.

• Electric charges cannot flow without water.

• Electric charges move through the water in the pool.

Some of the materials for a laboratory experiment are copper wire, plastic tubing, and a pair of cotton gloves. Why is the copper wire the best electrical conductor in this group of materials?

• Copper wire is easy to bend.

• Copper wire resists the flow of charged particles.

• Copper wire can withstand very high temperatures.

• Copper wire allows electric charges to flow easily through it.

A science lab has copper wire coated with rubber tubing, a plastic vial, and a pair of cotton gloves. Which of these materials is not an electrical insulator?

• copper wire

• cotton gloves

• plastic

• rubber tubing

An atom loses an electron. What will happen when it approaches a positively-charged ion?

• The ions will repel each other.

• The ions will attract each other.

• The ions will cancel each other out.

• The ions will neither attract nor repel each other.

A student is brushing her hair. As the hairbrush is brought near her head, the hair seems to reach toward the hairbrush. Which of the following is the best explanation?

• Two gravitational fields are interacting.

• Two magnetic fields are interacting.

• Two electric fields are interacting.

• Two electromagnetic fields are interacting.

Why is the magnetic force considered to be an action-at-a-distance force?

• Magnets must be far apart in order to exert a force.

• Magnets do not have to touch each other to experience a force.

• Magnets push each other apart to increase the distance between them.

• Magnets must be large in size in order to exert a force that is strong enough to notice.