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# Physics of Motion

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How and why do things move the way that they do? Be it a ball thrown in the air, or a train traveling across a track, everything follows specific rules when they're in motion. In physics, motion is described as a change in the position of an object throughout a period of time. Motion is capable of being both complex or simple, completely depending on what is being moved, and the environment it is in. The motion of an object is entirely affected by the forces acting on it at any given time, as well as forces that have acted on it in the recent past. For example, if I were to throw a ball and it was currently in mid-air, the push I gave that ball has already happened, but the effects of that force are still going to carry on until the motion of that ball has stopped.

Motion is completely dependent on the things around it, meaning it is relative. The fact that an object is moving or stationary is only true if everything around the object is also stationary to the person observing the stationary object. For example, a flag may be stationary on the Moon from the eyes of an astronaut, but the Moon is also orbiting the Earth, which in turn is orbiting the Sun, etc.

In physics, motion can be defined and calculated using a few variables that all bodies in motion have or can have: velocity, acceleration, displacement, and time. Velocity is the same as speed but depends on the direction a body is traveling, and the same can be said for displacement in terms of distance. Acceleration is the same as velocity but describes how much of a change in speed occurs over some time, instead of how much of a change in distance.

An example of a parabolic curve of a ball in motion, StudySmarter Originals

Gravity is a force that causes acceleration!

## What Formulas Do We Use When Calculating Motion?

When it comes to solving for any of these variables, we have five main equations that we can use:

The first is given as

This is the most simple formula, meaning that distance is equal to speed multiplied by time, only taking into account direction as well. This can only be used when acceleration is equal to 0.

The second equation is one of the three kinematic equations. Note that it does not depend on position.

Whereis the final velocity of an object,is its starting velocity,is the acceleration acting on it, andis the time that passes during motion.

Our third equation is another kinematic equation. This time it does not depend on the final velocity.

Where is the displacement. This formula can only be used if the acceleration on the object is positive.

Our fourth equation below is an easier way to calculate displacement when you know both the starting and final velocities that act on the object.

And our last equation is also the final kinematic equation. Note it does not depend on time :

Using these equations, we can solve for any particular variable we need to when studying an object in motion.

Since acceleration is a rate of change in velocity, We can find the average acceleration by taking the difference between our final velocity,and initial velocity,and dividing that over our time interval,In other words,

Where the bar abovesignifies average.

## What Are the Laws of Motion?

The laws defining the behavior of motion were first discovered and written by English physicist Sir Isaac Newton, and they apply to almost everything in the universe.

Some things do not follow these laws, such as objects traveling at close to the speed of light which follow Einstein's theory of relativity, and things smaller than atoms, which follow behaviors defined in the field of quantum mechanics.

### First Law: Law of Intertia

In simple terms, the first law of motion states that objects that are not being pushed will eventually come to rest. This means that if an object is experiencing no change in the forces acting on it, the object will tend towards a state of no movement, or rest.

This law was first discovered as a way to explain why don’t feel all the movement that goes on in the universe. We are standing on a planet that is spinning and moving around a sun that is moving around a galaxy, why can’t we feel all that movement? Well, since we are moving with the Earth as we are standing on it, we keep that motion constantly, and from our perspective, we are at rest.

### Second Law: F = ma

The second law of motion shows us that rate of change of the momentum of an object is exactly the same as the force that is being applied to it. In other words, if an object has a mass ofthe force acting on it is equal to its mass multiplied by its acceleration. This can be written as

### Third Law: Action & Reaction

The main way this law has been stated in the past is that every action has an equal and opposite reaction. This isn’t quite true, or just not quite informative enough. The third law of motion states that when two objects are to come into contact with each other, the forces that are applied to one another are equal in magnitude and opposite in direction.

For example, if an object is laying on the ground, the object is pushing down on the ground with its weight, which we know is a force. As we know of the third law of motion, we know that the ground is also pushing back, with a force equal to the weight and in the exact opposite direction.

## What Are the Types of Motion?

Movement occurs in a multitude of different ways, and the forces that are applied to objects in these different states of movement vary greatly. Here are a few types of motion:

### Linear Motion

Linear motion is straightforward, as it describes any form of movement that occurs in a straight line. This is the most basic form of motion. Nothing special or complicated has to occur when traveling from point A to point B.

### Oscillating Motion

Oscillating motion is a back and forth movement. Only when this movement is consistent over time can it be considered an oscillating motion. Waves, including sound waves, ocean waves, and radio waves are examples of oscillating motion. Waves use oscillating motion to store information in their amplitudes. Other common examples of oscillating motion are pendulums and springs.

A spring is a great example of an oscillating motion, Wikimedia Commons

### Rotary Motion

Rotary motion will move in a circular pattern. The use of this motion has been incredibly beneficial to use over time, with the use of the wheel to transport things, as well as many other real-world examples.

A diagram of rotary motion, showing the direction of velocity and acceleration. Brews ohare CC BY-SA 3.0

### Projectile Motion

Projectile motion is the movement of any object when thrown in an environment containing a gravitational field. If an object is thrown higher than horizontally, then the path it travels will form a curve, known as a parabola.

There is another lesser-known form of motion, irregular motion. This is a form of movement that doesn’t adhere to any fixed pattern, as the other forms of motion do.

## Physics of Motion - Key takeaways

• Motion in physics is a change in the position of an object or body over a time interval.

• Motion is relative, meaning that whether something is in motion or not depends on the state of motion of the bodies it is surrounded by.

• There are many formulas used to calculate variables that are relevant in motion, such as displacement, time, velocity, and acceleration.

• There are three laws of motion, the law of inertia, the law of F=ma, and the law of action & reaction.

• There are a few different types of motion, including linear, oscillating, and rotary motion.

## Frequently Asked Questions about Physics of Motion

Motion in physics can be described as a change in the position of a body over a period of time.

The 3 laws of motion are the law of inertia, the law of F=ma, and the law of action & reaction.

The different types of motion in physics are linear motion, oscillating motion, rotary motion, and irregular motion.

## Final Physics of Motion Quiz

Question

What are the forces applied on a book that is at rest on the table?

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Answer

1. The weight $$W$$ exerted by gravitational force on the book
2. The normal force $$N$$ exerted by the table on the book

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Question

What are the forces applied on a block suspended by a rope?

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Answer

1.  The weight $$W$$ exerted by gravitational force on the block.
2. The tension force $$T$$ exerted by the rope on the block.

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Question

What are the forces applied on a block that is placed on a table and being pushed by a force $$F_{a}$$ horizontally to the right?

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Answer

1. The weight $$W$$ exerted by the force of gravity on the block.
2. The normal force $$N$$ exerted by the table on the block.

3. The acting force $$F_{a}$$ that is pulling the block horizontally to the right.

4. The force of friction exerted by the table on the block in the opposite direction of motion (horizontally to the left).

Show question

Question

Each item in the issue requires a distinct free-body diagram.

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Answer

True.

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Question

A free body diagram is a valuable tool for evaluating all of the forces that operate on a body and studying its motion.

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Answer

True.

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Question

At each point of contact, there is always one applied force on the object in question.

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Answer

False.

At each point of contact, there is at least one force; there may be more.

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Question

The normal force acting on a body is always perpendicular to the point of contact.

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Answer

True.

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Question

In a free body diagram, the direction of acceleration is the opposite of the direction of the net force.

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Answer

False.

In a free body diagram, the direction of acceleration is the same as the direction of the net force.

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Question

The net force in a free body diagram can be zero.

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Answer

True.

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Question

If the net force applied to a system is zero, then the object is not acceleration.

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Answer

True.

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Question

If the component of the net force along the x-axis was positive:

Then the skier will be accelerating downward to the left.

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Answer

False.

The skier will be accelerating downward to the right.

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Question

Each vector force has two components, one along the x-axis and one along the y-axis.

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Answer

True.

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Question

Speed is a scalar quantity that describes the rate at which an object moves.

Is this statement true or false?

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Answer

True.

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Question

Is this statement true or false?

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Answer

False.

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Question

Physicists utilize the basic concepts of speed and velocity to describe the motion of objects in terms of :

Distance and Time.

Is this statement true or false?

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Answer

False.

Physicists utilize the basic concepts of speed and velocity to describe the motion of objects in terms of :

Distance, Time and Direction.

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Question

Delete this one please?

There is no difference between speed and velocity.

Is this statement true or false?

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Answer

False.

The two parameters differ.

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Question

Delete this one please?

While velocity is a scalar value, speed is a vector.

Is this statement true or false?

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Answer

False.

While speed is a scalar value, velocity is a vector.

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Question

Is this statement true or false?

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Answer

True.

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Question

We need to differentiate between the speed and average speed of an object since its speed may vary with time.

Is this statement true or false?

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Answer

True

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Question

The mean value of a body's speed over a period of time is called instantaneous speed.

Is this statement true or false?

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Answer

False.

The mean value of a body's speed over a period of time is called the "average speed."

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Question

To calculate the average speed, we divide the total distance traveled over the total time needed.

Is this statement true or false?

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Answer

True.

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Question

The speed can only be measured or expressed in:

kilometers per second (km/s),

Is this statement true or false?

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Answer

False.

The speed can be measured or expressed in:

• meters per second (m/s), where the distance will be expressed in meters and time in seconds.

• kilometers per hour (km/h), where the distance is measured in kilometers and the time in hours.

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Question

The average can only be calculated if the speed of the moving object is varied with time.

Is this statement true or false?

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Answer

True.

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Question

Is the angular velocity of something moving directly away from you zero or non-zero?

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Answer

Zero.

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Question

Is the angular velocity of something moving in a straight line that doesn't touch you zero or nonzero?

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Answer

Nonzero.

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Question

You are standing on a runway and a flying plane and a squirrel are both moving directly toward you. The angular velocity of which object is larger?

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Answer

Their angular velocities are equal.

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Question

Which of the following two objects will have a larger angular velocity with respect to your eyes? An ant walking full speed over your arm or a car driving full speed over a highway 10 km away?

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Answer

The ant.

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Question

The first scientist known to have put forward ideas about falling objects was Galileo.

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Answer

False.

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Question

According to Aristotle, heavy objects fall before light objects.

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Answer

True.

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Question

What was Galileo's experiment and what did he prove?

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Answer

Galileo performed an experiment that showed that two objects of different weights dropped at the same time from the Leaning Tower of Pisa fell to the ground almost simultaneously.

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Question

What is free fall?

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Answer

Free fall is a state of motion where objects fall only under the force of gravity.

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Question

Neglecting air resistance, if a stone and a paper cup are released from the same height at the same time, they will accelerate with equal gravitational acceleration and fall to the ground at the same time.

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Answer

True.

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Question

What experiment did astronaut David Scott perform?

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Answer

On August 2, 1971, astronaut David Scott conducted a free fall experiment on the Moon, dropping a hammer and a feather simultaneously. As predicted, they hit the lunar surface at the same time.

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Question

The acceleration of falling objects in an environment where air resistance is neglected is always the acceleration of gravity and does not depend on the mass of the object.

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Answer

True

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Question

Describe what mass is in basic terms.

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Answer

Mass is how much of something there is, or how much matter makes up something.

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Question

Does everything have mass?

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Answer

No, almost everything has mass, but things such as photons, which are light particles do not have mass.

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Question

What is the official unit of mass according to the International System of Units?

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Answer

Kilograms.

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Question

What is the difference between mass and weight?

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Answer

Mass is how much matter something is made up of, whereas weight is used to describe both the mass and the gravitational pull acting on a mass.

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Question

Would you weigh more or less on the Moon?

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Answer

You would weigh less on the Moon

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Question

Is mass a vector or a scalar unit?

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Answer

Mass is a scalar unit.

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Question

Is weight a vector or a scalar unit?

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Answer

Weight is a vector unit.

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Question

What is the principle that states that mass will always stay the same called?

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Answer

The Conservation of Mass.

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Question

Describe what density is in basic terms.

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Answer

Density is described as how much of something there is within a specific amount of space, or volume.

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Question

Describe what volume is in basic terms.

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Answer

Volume is the amount of space something fills.

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Question

Velocity is a scalar quantity.

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Answer

True

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Question

Velocity is defined as the...

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Answer

Rate of change of displacement (distance traveled in a particular direction) of an object with respect to time.

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Question

What is the instantaneous velocity of an object?

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Answer

Instantaneous velocity is the velocity of an object measured at a given instant in time.

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Question

The instantaneous velocity is equal to the average velocity...

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Answer

when the object travels at a uniform velocity

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Question

Which type of velocity is represented by the speedometer on your car?

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Answer

Instantaneous velocity

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Question

The velocity at any instant of time is known as ...

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Answer

Instantaneous velocity

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