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Lesson 1: Newton's First Law of Motion

Newton's First Law

In a previous unit of study, the variety of ways by which motion can be described (words, graphs, diagrams, numbers, etc.) was discussed. In this unit (Newton's Laws of Motion), the ways in which motion can be explained will be discussed. Isaac Newton (a 17th century scientist) put forth a variety of laws which explain why objects move (or don't move) as they do. These three laws have become known as Newton's three laws of motion. The focus of Lesson 1 is Newton's first law of motion - sometimes referred to as the "law of inertia."

Newton's first law of motion is often stated as

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

 

There are two parts to this statement - one which predicts the behavior of stationary objects and the other which predicts the behavior of moving objects. The two parts are summarized in the following diagram.

 

The behavior of all objects can be described by saying that objects tend to "keep on doing what they're doing" (unless acted upon by an unbalanced force). If at rest, they will continue in this same state of rest. If in motion with an eastward velocity of 5 m/s, they will continue in this same state of motion (5 m/s, East). If in motion with a leftward velocity of 2 m/s, they will continue in this same state of motion (2 m/s, left). The state of motion of an object is maintained as long as the object is not acted upon by an unbalanced force. All objects resist changes in their state of motion - they tend to "keep on doing what they're doing."

 

Remember the Pass the Water lab performed in class? Students participated in a relay race, carrying a plastic container of water around a race track. The water had a tendency to spill from the container during specific locations on the track. In general the water spilled when:

• the container was at rest and you attempted to move it
• the container was in motion and you attempted to stop it
• the container was moving in one direction and you attempted to change its direction.
  

The water was spilled whenever the state of motion of the container was changed. The water resisted this change in its own state of motion. The water tended to "keep on doing what it was doing." The container was moved from rest to a high speed at the starting line; the water remained at rest and spilled onto the table. The container was stopped near the finish line; the water kept moving and spilled over container's leading edge. The container was forced to move in a different direction to make it around a curve; the water kept moving in the same direction and spilled over its edge. The behavior of the water during the relay race can be explained by Newton's first law of motion.

 

Everyday Applications of Newton's First Law

There are many applications of Newton's first law of motion. Consider some of your experiences in an automobile. Have you ever observed the behavior of coffee in a coffee cup filled to the rim while starting a car from rest or while bringing a car to rest from a state of motion? Coffee tends to "keep on doing what it is doing." When you accelerate a car from rest, the road provides an unbalanced force on the spinning wheels to push the car forward; yet the coffee (which was at rest) wants to stay at rest. While the car accelerates forward, the coffee remains in the same position; subsequently, the car accelerates out from under the coffee and the coffee spills in your lap. On the other hand, when braking from a state of motion the coffee continues forward with the same speed and in the same direction, ultimately hitting the windshield or the dash. Coffee in motion tends to stay in motion.

Have you ever experienced inertia (resisting changes in your state of motion) in an automobile while it is braking to a stop? The force of the road on the locked wheels provides the unbalanced force to change the car's state of motion, yet there is no unbalanced force to change your own state of motion. Thus, you continue in motion, sliding along the seat in forward motion. A person in motion tends to stay in motion with the same speed and in the same direction ... unless acted upon by the unbalanced force of a seat belt. Yes, seat belts are used to provide safety for passengers whose motion is governed by Newton's laws. The seat belt provides the unbalanced force which brings you from a state of motion to a state of rest. Perhaps you could speculate what would occur when no seat belt is used.

 

 

 

There are many more applications of Newton's first law of motion. Several applications are listed below - it is hoped that you could provide explanations for each application.

• blood rushes from your head to your feet while quickly stopping when riding on a descending elevator.
• the head of a hammer can be tightened onto the wooden handle by banging the bottom of the handle against a hard surface.
• a brick is painlessly broken over the hand of a physics teacher by slamming it with a hammer. (CAUTION: do not attempt this at home!)
• to dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down and, thrusted downward at high speeds and then abruptly halted.
• headrests are placed in cars to prevent whiplash injuries during rear-end collisions.
• while riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or rock or other object which abruptly halts the motion of the skateboard.

And perhaps you remember a few demonstrations performed in class which further illustrate applications of Newton's first law.

 

Self Portrait (JPEG - 18k)
Leonardo was born near the little town of Vinci, Italy, which is very close to Florence, on April 15, 1452. His father was Ser Piero da Vinci, and his mother was a local peasant girl named Caterina. When young Leonardo was only one year old, his father married another woman, and his mother married a peasant man and disappeared. At an early age, Leonardo showed many extraordinary talents. He was very interested in just about everything around him. He was said to have confused his math teachers with his questions, played the lute and sung with great talent, and above all, was incredibly good at drawing.

At the time, I was the leading Florentine artist, and one of his father's good friends. After taking one look at Leonardo's breathtaking drawings, I offered him a job as an apprentice at my studio. At this time Leonardo was about 15 years old, and I was working on a project of great prestige. This project was making the gilded copper globe that tops the Florence Cathedral, the building that is the pride and joy of the Florentines. I kept Leonardo very busy doing common apprentice jobs, from preparing materials to help paint pictures. I noticed that he did these with extreme gift, and that he was much more capable then any of my other apprentices. Soon I noticed that Leonardo's talent was so great, I would never be able to match his painting talents. I gave up painting and concentrated on sculptures, certain that I was making the right career move.

Mona Lisa (JPEG - 13K)

Besides being an incredible artist, Leonardo was also a very handsome, caring, and good-natured person. He had a great love for animals, and kept his very own horses. A story I find very interesting, and I am sure you will too, is that one day, in the markets, Leonardo bought some caged birds and began to set them free. But this did not stop at just one kind act. Leonardo soon bought many caged birds and did the same thing with each of them. Leonardo was also incredibly strong. People say that he could bend a horseshoe with his bare hands.

In 1481 or 1482, Leonardo moved from Florence to Milan, which is the greatest city in northern Italy. He was invited by Duke Lodovico Sforza, to whom Leonardo had written a remarkable letter. In this letter, Leonardo promoted himself as a fine designer of war machines, and added that he was an architect, sculptor, and a fine painter.

Leonardo spent most of the next 20 years under Lodovico's rule, which during this period he designed stage machinery, mechanical toys, played the lute, sang, told riddles and jokes, and basically, entertained the Duke. But during his busy schedule, he always seemed to find time to sketch a drawing. He would wander thoughout the streets of Milan, drawing everyone he found worthy enough to draw.

I might not want a large amount of text on my home page if I want to guide visitors toward my other pages. Instead of text, I can add others' buttons to this first page, and I'll be rewarded for people who click on the buttons. For example, if a visitor signs up for a Visa using the NextCard button on my site, I earn at least $20!

Even if I don't put much text on my home page, it's a good idea to include hidden tools that will help me promote my site, so people other than my friends and family actually see it. For example, I could add meta tags, which are hidden codes that allow search engines to find my site. I could also install stats and a counter so I know how many people are visiting. If not many are visiting, submitting my site to search engines will guide more traffic to my site.