# Physical Science Test I

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Chapters 1,2,3

### What are two components of a measurement Statement?

a number and the name of the unit.

### What does each component of a measurent statement tell you?

The number tells "how many" and the unit explains "of what"

meter

### Does the Density of a liquid change with the shape of a container?Explain.

no, density is a ration of mass per unit volume, as long as this ratio stays the same, the density does not change.

### What is an equation?

mathematical statement that describes a relationship where the quantities on one side are identical to the quantities on the other side.

### How are equations used in the physical sciences?

describe quantities, define concepts, and show how quantities change together.

### Compare and Contrast a Scientific principle and a scientific law.

SP-explains a narrow range of observations,SL-describes many general phenomena. Principles can usually be explained in terms of laws.

### Are all theories always completely accepted or completely rejected?Explain.

not always completely accepted but are rarely rejected completely. The better a theory explains the results of experiments and correctly predicts the results of new experiments, the greater the degree of acceptance. Theories that do not conform to experiments are usually modified and gain wider acceptance.

kilograms

second

### Disregarding air friction, describe all the forces acting on a bullet shot from a rifle into the air.

After it leaves the rifle barrel, the force of gravity acting straight down is the only force acting on the bullet.

### Can gravity act in a vaccum? Explain.

Gravity does not depend upon some medium so it can operate in a vaccum.

### Is it possible for a small car to have the same momentum as a large truck?Explain.

Yes, the small car would have to be moving with a much higher velocity, but it can have the same momentum since monmentum is mass times velocity.

### Why should you bend your knees as you hit the ground after jumping from a roof?

Bending your knees as you hit the ground extends the stopping time. This is important since the change of momentum is equal to the impulse, which is force times the time. A greater time therefore means less force when coming to a stop.

### Is it possible for your weight to change while your mass remains constant?Explain.

Your weight can change from place to place because weight is a downward force from gravitational attraction on your mass and the force of gravity can vary from place to place.

### What maintains the speed of Earth as it moves in it's orbit around the sun?

Nothing! there is no force parallel to the motion to increase or decrease the earth's speed, so the speed remains constant.

### Suppose you are standing on the ice of a frozen lake and there is no friction what so ever. How can you get off the ice?(Hint: Friction is necessary to crawl or walk, so that will not get you off the ice.)

If you have something to throw,such as car keys or a snowball, you can easily get off the frictionless ice. Since the force you apply to the thrown object results in an equal and opposite force(3rd law) you will move in the opposite direction as the object is thrown(2nd law). The same result can be achieved by blowing a puff of air in a direction opposite to the way you wish to move.

### How is work related to energy?

Energy is the ability to do work, and doing work on something gives it energy.

### What is the relationship between the work done while moving a book to a higher bookshelf and the potential energy that the book as on the higher shelf?

The work done is equal to the increase in gravitational potential energy.

### Does a person standing motionless in the aisle of a moving bus have kinetic energy? Explain.

Relative to the bus, the person has no kinetic energy because the person is at rest relative to the bus. Relative to the ground, however, the person does have kinetic energy because the person is moving with the same speed as the bus.

### If energy cannot be destroyed, why do some people worry about the energy supplies?

Energy is eventually converted into unrecoverable radiant energy, so new sources of convertible energy must be found in order to continue performing useful work.

### A spring clamp exerts a force on a stack of papers it is holding together. Is the spring clamp doing work on the papers?Explain.

If the spring clamp does not cause the paper to move, it is not acting through a distance and no work is done.

### Compare the energy needed to raise a mass 10m on Earth to the energy needed to raise the same mass 10m on the Moon. Explain the difference, if any.

The energy required is less on the moon because the weight of the object (the downward force due to gravity) depends upon the force of gravity, which is less on the moon than on the earth. Less energy is needed to do the work of raising the mass on the mon, and the elevated object on the moon has less potential energy as a consequence of the work done.

### What happens to the kinetic energy of a falling book when the book hits the floor?

The energy is converted to heat and sound.

### Newton's First Law of Motion

Every object retains its state of rest or its state of uniform straight-line motion unless acted upon by an unbalanced force.

### Newton's Second Law of Motion

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to the mass of the object.

### Newton's Third Law of Motion

Whenever two object interact, the force exerted on one object is equal in size and opposite in direction to the force exerted on the other object.

Example: