# when a moving object comes to rest and body to move, which changes the speeds of object?

### Mohammed

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## Newton’s Laws

## Newton’s Laws

Newton’s Laws The First Law: Inertia

Newton’s first law of motion describes inertia. According to this law, a body at rest tends to stay at rest, and a body in motion tends to stay in motion, unless acted on by a net external force.

### LEARNING OBJECTIVES

Define the First Law of Motion

### KEY TAKEAWAYS

### Key Points

Newton’s three laws of physics are the basis for mechanics.

The first law states that a body at rest will stay at rest until a net external force acts upon it and that a body in motion will remain in motion at a constant velocity until acted on by a net external force.

Net external force is the sum of all of the forcing acting on an object.

Just because there are forces acting on an object doesn’t necessarily mean that there is a net external force; forces that are equal in magnitude but acting in opposite directions can cancel one another out.

Friction is the force between an object in motion and the surface on which it moves. Friction is the external force that acts on objects and causes them to slow down when no other external force acts upon them.

Inertia is the tendency of a body in motion to remain in motion. Inertia is dependent on mass, which is why it is harder to change the direction of a heavy body in motion than it is to change the direction of a lighter object in motion.

### Key Terms

**inertia**: The property of a body that resists any change to its uniform motion; equivalent to its mass.**friction**: A force that resists the relative motion or tendency to such motion of two bodies in contact.**uniform motion**: Motion at a constant velocity (with zero acceleration). Note that an object in motion will not change its velocity unless an unbalanced force acts upon it.

### History

Sir Isaac Newton was an English scientist who was interested in the motion of objects under various conditions. In 1687, he published a work called Philosophiae Naturalis Principla Mathematica, which described his three laws of motion. Newton used these laws to explain and explore the motion of physical objects and systems. These laws form the basis for mechanics. The laws describe the relationship between forces acting on a body and the motions experienced due to these forces. The three laws are as follows:

If an object experiences no net force, its velocity will remain constant. The object is either at rest and the velocity is zero or it moves in a straight line with a constant speed.

The acceleration of an object is parallel and directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.

When a first object exerts a force on a second object, the second object simultaneously exerts a force on the first object, meaning that the force of the first object and the force of the second object are equal in magnitude and opposite in direction.

### The First Law of Motion

You have most likely heard Newton’s first law of motion before. If you haven’t heard it in the form written above, you have probably heard that “a body in motion stays in motion, and a body at rest stays at rest.” This means that an object that is in motion will not change its velocity unless an unbalanced force acts upon it. This is called uniform motion. It is easier to explain this concept through examples.

### EXAMPLES

If you are ice skating, and you push yourself away from the side of the rink, according to Newton’s first law you will continue all the way to the other side of the rink. But, this won’t actually happen. Newton says that a body in motion will stay in motion until an outside force acts upon it. In this and most other real world cases, this outside force is friction. The friction between your ice skates and the ice is what causes you to slow down and eventually stop.

Let’s look at another situation. Refer to for this example. Why do we wear seat belts? Obviously, they’re there to protect us from injury in case of a car accident. If a car is traveling at 60 mph, the driver is also traveling at 60 mph. When the car suddenly stops, an external force is applied to the car that causes it to slow down. But there is no force acting on the driver, so the driver continues to travel at 60 mph. The seat belt is there to counteract this and act as that external force to slow the driver down along with the car, preventing them from being harmed.

**Newton’s First Law**: Newton’s first law in effect on the driver of a car

### Inertia

Sometimes this first law of motion is referred to as the law of inertia. Inertia is the property of a body to remain at rest or to remain in motion with constant velocity. Some objects have more inertia than others because the inertia of an object is equivalent to its mass. This is why it is more difficult to change the direction of a boulder than a baseball.

**Doc Physics – Newton**: Newton’s first law is hugely counterintuitive. You may have learned it in gradeschool, though. Let’s see it for the mind-blowing conclusion it really is.

## The Second Law: Force and Acceleration

The second law states that the net force on an object is equal to the rate of change, or derivative, of its linear momentum.

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## Newton's laws of motion (article)

Forces

## Newton's laws of motion

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In the final example of the last section, we saw how we could calculate a dynamic acceleration based on a vector pointing from a circle on the screen to the mouse position. The resulting motion resembled a magnetic attraction between circle and mouse, as if some force were pulling the circle in towards the mouse.

In this section, we will formalize our understanding of the concept of a force and its relationship to acceleration. Our goal, by the end of this, is to understand how to make multiple objects move around the screen and respond to a variety of environmental forces.

Before we begin examining the practical realities of simulating forces in code, let’s take a conceptual look at what it means to be a force in the real world. Just like the word “vector,” “force” is often used to mean a variety of things. It can indicate a powerful intensity, as in “She pushed the boulder with great force” or “He spoke forcefully.” The definition of **force** that we care about is much more formal and comes from Isaac Newton’s laws of motion:

**A force is a vector that causes an object with mass to accelerate.**

The good news here is that we recognize the first part of the definition: a force is a vector. Thank goodness we just spent a whole section learning what a vector is and how to program with PVectors!

Let’s look at Newton's three laws of motion in relation to the concept of a force.

### Newton’s First Law

Newton’s first law is commonly stated as:

**An object at rest stays at rest and an object in motion stays in motion.**

However, this is missing an important element related to forces. We could expand it by stating:

**An object at rest stays at rest and an object in motion stays in motion at a constant speed and direction unless acted upon by an unbalanced force.**

By the time Newton came along, the prevailing theory of motion—formulated by Aristotle—was nearly two thousand years old. It stated that if an object is moving, some sort of force is required to keep it moving. Unless that moving thing is being pushed or pulled, it will simply slow down or stop. Right?

This, of course, is not true. In the absence of any forces, no force is required to keep an object moving. An object (such as a ball) tossed in the earth’s atmosphere slows down because of air resistance (a force). An object’s velocity will only remain constant in the absence of any forces or if the forces that act on it cancel each other out, i.e. the net force adds up to zero. This is often referred to as **equilibrium**. The falling ball will reach a terminal velocity (that stays constant) once the force of air resistance equals the force of gravity.

Diagram of two people blowing on pendulum

The pendulum doesn't move because all the forces cancel each other out (add up to a net force of zero)

In our ProcessingJS world, we could restate Newton’s first law as follows:

**An object’s PVector velocity will remain constant if it is in a state of equilibrium.**

Skipping Newton’s second law (arguably the most important law for our purposes) for a moment, let’s move on to the third law.

### Newton’s Third Law

This law is often stated as:

**For every action there is an equal and opposite reaction.**

This law frequently causes some confusion in the way that it is stated. For one, it sounds like one force causes another. Yes, if you push someone, that someone may actively decide to push you back. But this is not the action and reaction we are talking about with Newton’s third law.

Let’s say you push against a wall. The wall doesn’t actively decide to push back on you. There is no “origin” force. Your push simply includes both forces, referred to as an “action/reaction pair.”

A better way of stating the law might be:

**Forces always occur in pairs. The two forces are of equal strength, but in opposite directions.**

Now, this still causes confusion because it sounds like these forces would always cancel each other out. This is not the case. Remember, the forces act on different objects. And just because the two forces are equal, it doesn’t mean that the movements are equal (or that the objects will stop moving).

Try pushing on a stationary truck. Although the truck is far more powerful than you, unlike a moving one, a stationary truck will never overpower you and send you flying backwards. The force you exert on it is equal and opposite to the force exerted on your hands. The outcome depends on a variety of other factors. If the truck is a small truck on an icy downhill, you’ll probably be able to get it to move. On the other hand, if it’s a very large truck on a dirt road and you push hard enough (maybe even take a running start), you could injure your hand.

What if you pushed a truck while wearing roller skates?

A man pushing a truck while wearing roller skates

Let's re-state Newton's third law for our ProcessingJS world:

**If we calculate a PVector f that is a force of object A on object B, we must also apply the force—PVector.mult(f,-1);—that B exerts on object A.**

## Motion and Forces: Newton's First Law of Motion

This physical science activity explores motion and force with students who are visually impaired to help them better understand Newton's First Law of Motion.

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## Motion and Forces: Newton's First Law of Motion

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By Accessible Science on Nov 07, 2014

Related Courses Teaching Science Self-paced

Teaching Science to Young Children With Visual Impairments

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The activity described below gets everyone’s attention! Students with a visual impairment benefit from a chance to feel the weight of the various items placed on the tablecloth, as well as a chance to examine the table before and after the table cloth is pulled.

### Vocabulary

Inertia – the tendency of an object to keep its motion

### Inertia

Place a book on your desk. Does the book move? Unless you push the book, it will stay put just the way you left it. Imagine a spacecraft moving through space. When the engines are turned off the spacecraft will coast through space at the same speed and in the same direction. The book and spacecraft have inertia. Because of inertia, an object at rest rends to stay at rest. An object in motion tends to keep moving at a constant speed in a straight line.

### Newton's First Law

Newton’s first law of motion explains how inertia affects moving and nonmoving objects. Newton’s first law states that an object will remain at rest or move at a constant speed in a straight line unless it is acted on by an unbalanced force. According to Newton’s first law, an unbalanced force is needed to move the book on your desk. You could supply the force by pushing the book. An unbalanced force is needed to change the speed or direction of the spacecraft. This force could be supplied by the spacecraft’s engine.

### Effects of Interia

You can see the effects of inertia everywhere. In baseball, for example, to overcome inertia a base runner has to “round” the bases instead of making sharp turns. As a more familiar example of inertia, think about riding in a car. You and the car have inertia. If the car comes to a sudden stop, your body tends to keep moving forward. When the car starts moving again, your body tends to stay at rest. You move forward because the car seat exerts an unbalanced force on your body.

## Materials

Table cloth

2 unbreakable plates

2 unbreakable cups

2 forks, spoons, napkins

The heavier the cups and plates, the better it works A textbook

## Procedure

Start with the table cloth on a table or desk.

Set the table as if for dinner.

Notice the difference in mass of each object. The book has the most mass and the napkin has the least.

Try the magician’s trick of grabbing the edges of the table cloth and then quickly jerk it out from under the items on the table.

Hopefully you’ll notice that the napkin flew off (less inertia), and things like the silverware, plates and book stayed put.

### Questions and Conclusions

In space, a spacecraft with its engines turned off will move with constant speed in the same __.

A book will not move by itself because it has __.

A book will remain at rest unless it is acted on by an __ force.

When a car stops suddenly, your body tends to keep moving __.

Newton’s first law explains how inertia affects moving and __ objects.

MakingScienceAccessible.pdf

## NGSS Standards:

**Motion and Forces:**

The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change. The greater the mass of the object, the greater the force needed to achieve the same change in motion. For any given object, a larger force causes a larger change in motion. (MS-PS2-2)

PS2.A: Forces and motion: The role of the mass of an object must be qualitatively accounted for in any change of motion due to the application of a force. (Grades 6-8)

Article and activity adapted from Concepts and Challenges: Physical Science, Fourth Edition. Parsippany, NJ: Globe Fearon Inc., Pearson Learning Group, 2009, pages 280 to 281.

Purchase the full book here or download the FREE PDF for this activity.

Attached File(s):

MakingScienceAccessible.pdf

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