# How Much Do You Know About the Classical Mechanics of Physics?

SCIENCE

By: Ryan Choate

7 Min Quiz

Image: Martin Steinthaler / Moment / Getty Images

## About This Quiz

Classical mechanics is the study of objects in motion, including a state of non-motion. Sometimes referred to as Newtonian mechanics, classical mechanics analyzes why things move (or don't move) the way they do. Like you may have guessed from the name, Isaac Newton was instrumental in developing the knowledge in this field. His three laws of motion are instrumental building blocks of classical mechanics.

Newton's 1st Law of Motion states that a body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an unbalanced force. This one explains the importance of wearing a seatbelt. Without a seatbelt to exert a force, a driver or passenger will continue his or her forward motion until hitting something else, often the pavement. Newton's 2nd Law states that the net force acting on an object is equal to the mass of that object times its acceleration. This is better summed up in the famous equation, F = ma. Newton's 3rd Law states that for every action, there is an equal and opposite reaction. Without this law, we would have never been able to launch a rocket and explore space!

Several other scientists have contributed to the field of classical mechanics as well. Galileo Galilei, Julius Robert Mayer, Daniel Bernoulli and many others have lent their superb observational and mathematical skills to the development of the physics of motion. Classical mechanics is the backbone of physics, astronomy and engineering. Scientists will continue to make incredible discoveries thanks to the laws and principles making up this branch of science. May the mass times acceleration be with you on this quiz!

# What kind of potential energy does an object have because of its height above the ground?

Gravitational potential energy is the energy an object possesses because of its height above the ground. Gravitational PE can be calculated by multiplying the mass, height, and acceleration due to gravity (9.8 m/s2) together.

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# Which of the following forces is NOT one of the four fundamental forces that apply in our universe?

Everything with mass possesses a gravitational force. Electromagnetism holds atoms together. The strong force holds the nucleus of atoms together. The weak force is responsible for radioactive decay. Without these fundamental forces, you and all the other matter in the universe would fall apart.

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# Which of the following is a unit of force?

A newton is equal to the force that would give a mass of 1 kg an acceleration of 1 m/s2. A joule is a measure of energy or work, m/s2 is a measure of acceleration, a watt is a measure of power in an electric circuit, and a kilogram is a unit of mass.

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# If the sun suddenly collapsed to become a black hole, the Earth would?

The mass of the sun wouldn’t change. A black hole contains the same mass, but in a more condensed version. Since gravitational force only depends on the mass of the two objects being attracted to each other and their distance apart, there will be no change in the Earth’s orbit.

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# What kind of energy does an object possess because of its position, condition or chemical makeup?

If an object has the potential to move, then it has potential energy. A ball held in the air by someone has the potential to move if that person releases it. If a stretched rubber band is released, it will move. Muscles can harness the power of chemical bonds in order to contract. Once an object begins moving, its potential energy is converted into kinetic energy.

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# What change does an unbalanced force on an object cause?

An unbalanced force causes an acceleration, a relationship seen in Newton’s 2nd Law of motion (F = ma). An acceleration is any change in velocity.

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# Which scientist is reputed to have dropped balls of different masses off the Leaning Tower of Pisa in order to see the effects of the gravity?

Between 1589 and 1592, Galileo is reported to have dropped two balls of different masses from the Leaning Tower of Pisa in order to demonstrate a consistent acceleration regardless of their masses. All objects, when able to disregard air resistance, fall to Earth at the same rate.

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# What type of energy is found within every moving object?

An object is able to do work on another object if it is moving. Any object with motion possesses at least some kinetic energy.

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# What happens to an astronaut if he throws a hammer while in outer space?

Newton’s 3rd Law states that, "For every action, there is an equal and opposite reaction.” The astronaut exerts a force on the hammer, and the hammer exerts an equal and opposite force on the astronaut. This causes the astronaut to begin moving in the opposite direction of the hammer.

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# What is the acceleration due to the force of gravity here on Earth?

Every object, if neglecting air resistance, falls to Earth with an acceleration of 9.8 m/s2. As an object’s mass increases, the force of gravity also increases, allowing it to accelerate at the same rate.

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# A truck driving down the highway hits a bug. The force of impact is what?

Newton’s third law states that for every action there is an opposite and equal reaction. The truck experiences the same force as the bug, but because of its larger mass, experiences a smaller change in velocity (practically zero) so therefore experiences less damage.

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# Which law of physics makes a perpetual motion machine impossible?

The 1st Law of Thermodynamics applies to the conservation of energy. This principle states that energy cannot be created or destroyed, only converted from one form to another. Since no machine can operate completely without friction, there is always some kinetic energy “lost” to heat. Because of this, every machine will need some form of energy input in order to keep going.

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# What term describes the use of force to move an object in the direction of the force?

In physics, work is said to be done when a force causes a displacement. If there is no movement, then there is no work. You push against a building as hard as you can until you’re completely exhausted - but if that building doesn’t move, then you haven’t done any work.

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# Which of the following objects possesses the most inertia?

The semi-truck has the most mass, and therefore the most inertia. It will require more force to accelerate, whether trying to slow it down, speed it up or change its direction.

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# What term describes the ability to do work?

An object (including a person) can only do work if that object possesses energy. This does not apply to your brain needing coffee in the morning in order to function!

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# When at rest on the launching pad, the force of gravity acting on the space shuttle is quite large. Once in orbit, about 250 miles above the earth, what is the force of gravity acting on the shuttle?

The force of gravity acting on an object depends on three things: the object’s mass, the Earth’s mass and the object’s distance from the Earth’s center. The mass of the object and the mass of Earth remain unchanged. The distance of the shuttle from the center of Earth only changes by about 4% (3958 miles from the center while on the surface, to 4158 miles when in orbit)

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# Which would be more damaging: driving head-on into a concrete wall or driving head-on into a car of equal mass and going an equal speed?

The change in momentum is equal either way. If the car traveling toward you had a higher speed, it would bring your car to a stop and then send you backward, equalling a larger change in momentum and thus more damage. If the car traveling toward you had a lower speed, then you would come to a stop more slowly, pushing that car backward. The collision would have more “give” and therefore less damage. Since the car has the same speed, the change in momentum, and therefore the damage would be the same as running into a concrete wall.

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# What is the acceleration of a ball thrown directly upward when it reaches the very top of its trajectory?

The acceleration due to gravity is 9.8 m/s2 for all objects on Earth. The velocity of the ball will be 0 m/s at that instant, but remember that acceleration is the rate at which velocity changes. Right before the ball reaches the top, it has upward velocity, but is slowing down to zero, at which point it will begin a downward velocity, speeding up.

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# When a gun is fired, what is the momentum of the recoiling gun as compared to the momentum of the bullet?

More than just a bullet comes out of the gun when it is fired. Gas also leaves the gun, which also has mass and therefore momentum - especially when traveling at such a high speed. So the momentum of the recoiling gun is equal to the momentum of the bullet PLUS the momentum of the gases.

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# You brake suddenly while driving your car. The passengers in your car lurch forward. This demonstrates what?

Newton’s 1st Law (commonly referred to as the Law of Inertia) states that an object in motion stays in motion unless acted upon by an unbalanced force. Because the braking force is only exerted on the car and not on the passengers, the passengers’ inertia will carry them forward at the same speed and in the same direction until another force acts on them - which is exactly what seat belts do.

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# Imagine you are standing on top of a moving parade float. It is moving at a constant pace. You jump up in the air as high as you can. Where will you land?

Newton’s 1st Law states that any object, including you, will continue in a straight line of motion at the same speed unless acted upon by an outside force. Because there is no force acting on your horizontal motion, you will continue to travel at the same speed that you were going when you were standing on the float.

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# An object is moving in a circle with constant speed. Is the object accelerating?

The definition of acceleration is a change in velocity. This means that any change in speed, speeding up or slowing down, or any change in direction means that an object is accelerating. An object traveling in a circle is constantly changing its direction.

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# A roller coaster travels on a frictionless track. The total energy of the roller coaster car at the top of the tallest hill is 25,000 joules. What is its total mechanical energy at the bottom of that hill?

The total mechanical energy remains the same as long as no work is done on the system. This is the Law of Conservation of Energy. The energy changes forms as the roller coaster car travels - it is mostly potential energy at the top of the hill and mostly kinetic at the bottom, but the total energy remains the same.

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# A man weighs 200 pounds. He stands on two bathroom scales with a foot on each one so that his weight is equally distributed. What is the reading on each scale?

As long as the man’s center of mass is directly between the two scales, the force exerted on the scales should be split evenly. One hundred pounds of force on each scale will add to his total weight of 200 pounds.

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# A railroad car is at rest. It's then hit by an identical railroad car traveling with a momentum of 100 units. The cars stick together and move down the railroad tracks. The combined momentum of the two railroad cars after the collision is what?

Due to the Law of Conservation of Momentum, the resulting momentum must equal the initial momentum. Since the first railroad car starts at rest with no velocity, it therefore has no momentum. This makes the momentum of the entire initial railroad car system 100 units. The resulting momentum must be the same.

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# A cannon ball traveling at 20 m/s has a momentum of 80 kg·m/s. What is the mass of the ball?

Momentum is the product of mass and velocity. A mass of 4 kg multiplied by a velocity of 20 m/s gives you a total momentum of 80 kg·m/s.

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# Imagine that you are in outer space, away from other planets or any atmosphere. If you had a box and gave it a push, what do you think would happen?

The box will move forever. Since there are no forces acting on the box after you’ve pushed it, it will continue to move in a straight line at a constant speed, keeping in accordance with Newton’s 1st Law.

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# You are holding a heavy bowling ball. Your friend is holding a lighter basketball. You both drop the balls from the same height. The balls hit the ground at the same time. Why?

All mass accelerates at a rate of 9.81 m/s2 here on Earth, disregarding air resistance. In order for the larger mass to accelerate at the same rate as the smaller mass and hit the floor at the same time, the force of gravity must be greater on it.

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# Your high school teacher places a wooden block and a bucket of water side by side on a bathroom scale. He records the total weight of the objects. Then your teacher places the wooden block in the bucket of water. What will happen to the total weight that reads on the scale?

The total will remain the same. The block appears to weigh less in the water due to the upward buoyant force by the water on the block, but the total weight of the system is the same. The force by the water upward on the block is balanced by the force by the block on the water.

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# How can you increase the number of times a pendulum swings in 30 seconds by changing only one thing?

Adding more weight (or mass) does not matter. All objects fall with the same acceleration. The initial height of the swing doesn’t matter, either. The higher the swing, the more distance the bob has to travel, but it also moves faster. The time it takes for the bob to swing back to its point of release depends only on length of the string, which shortens the distance of the center of mass to the point of support.

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# How much does the sky weigh?

The earth has a surface area of 7.88 x 1017 square inches. The average atmospheric pressure is 14.7 lbs per square inch. Multiplied together, that gives you a weight of 5.2 million billion metric tons.

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# What happens to the boiling point of water when exposed to a lower air pressure?

A liquid boils when its vapor pressure equals the pressure of the gas surrounding it. If the pressure of the surrounding gas lowers, then so does the boiling point.

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# Which of the following is a unit of power?

The watt is a unit of power. It is equal to 1 joule per second. A newton is a unit of force, a joule is a unit of work or energy, and a kelvin is a unit of temperature.

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# How fast does sound travel?

Sound travels at 343 m/s as it propagates through air at standard temperature and pressure. As air cools, sound will travel slower.

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# Which law states, “An object at rest will remain at rest and an object in motion will remain in motion, unless acted upon by an unbalanced force.”

This law is also referred to as the Law of Inertia. Inertia is an object’s resistance to a change in its motion. This mean that all objects “want” to keep doing what they are doing. It takes a force to cause an acceleration, whether that means speeding up, slowing down, changing directions, etc.

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