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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.

What does it mean in real world terms?

Have you ever been riding in a car when the driver suddenly slammed on the brakes? How did your body move as the car came to a stop? You probably felt your body move forward. When you felt this happening you experienced Newton's first law of motion.In the car your body was in motion, traveling at the same speed as the car. When the car stopped, your body stayed in motion. If you were not wearing a seatbelt and you were traveling very fast, your body could continue to move forward through the windshield!

Similiary , when you are in a car at rest to begin with and when the car starts moving suddenly ,your body is pushed back, on to the seat.This is because of your body's tendency to remain at rest. It finally moved as an external force was acting on it, in the form of the car moving forward underneath it.

To consider another example, imagine yourself riding a bike.Its Newton's first law that would explain the phenomenon of your bike rolling on even when you stopped pedalling.Your bike would have never stopped if it hadn't been for the friction acting on the tyres of your bike , from the track, and air friction acting on the entire bike.

Newton called his first law, inertia. Inertia is the property of an object to remain at constant velocity unless acted upon by an outside force.By constant velocity we also mean that it will continue to be in rest, if it were in rest (v=0) to begin with.This law , hence is also called the law of inertia.

Haven't you seen a magician pull a cloth from a table without disturbing the dishes and the cutlery? Neat, eh?

The magician performing this trick wasn’t really using magic; he or she just had a good understanding of a scientific principle called inertia. The plates, glasses, and silverware on the table in the magic trick all have inertia. Pulling the tablecloth is an outside force acting on those objects. If the outside force acts quickly enough, the inertia of the objects keeps them from moving. In order for the trick to be successful, the tablecloth has to be yanked out very quickly while the inertia of the objects on top of the table keeps them in place. In addition, the “slippery” tablecloth lessens the force. Imagine if the magician used sand paper instead of a tablecloth; he or she then wouldn’t be able to pull it out fast enough to avoid causing the items on the table to move.

A force is a push or a pull.Forces are described not only by how strong they are, but also by the direction in which they act. When two forces are exerted in the same direction,they add together.When forces are exerted in opposite directions, a force exerted in one direction is assigned a positive number and a force exerted in the other direction is assigned a negative number.The overall force on an object,called the net force, is found by adding the forces together.There can be any number of forces exerted on an object. When there is a net force acting on an object, the force is said to be unbalanced.An unbalanced force can cause an object to start moving, stop moving, or change direction. An unbalanced force acting on an object will change the object’s motion. Equal forces acting on an object in opposite directions are called balanced forces.Balanced forces acting on an object will not change the object’s motion.When you add equal forces exerted in opposite directions,the net force is zero.

1.Write a paragragh explaining how safety features like airbags and seat belts are necessary. Explain in terms of Newton's laws?

2.An astronaut in outer space away from gravitational or frictional forces throws a rock. Describe in detail the motion of the rock and explain why it moves that way.

3.This experiment will teach you more about why Newton’s First Law of Motion is also called the Law of Inertia. The method used in this experiment is very similar to one that Galileo conducted.

Activity

• two identical jars with lids (either plastic or glass jars)
• flour or sand to fill one of the jars
• iron filings or small lead pellets to fill one of the jars
• two identical, empty three-ring binders (at least 2.5” in width)
• a measuring tape

1. Fill one jar with flour or sand. Pack it tightly.
2. Fill the other jar with iron filings or small lead pellets. Again, fill it tightly.
3. Put lids on both of the jars. Lids should be on tight.
4. Place both three-ring binders next to each other on a wooden or tile floor. Place each jar on
its side and release both from the top of the “ramps” at exactly the same time.
5. In the Table below, record how far each jar rolled. Do not measure the binder itself, just the
distance from the end of the binder to where each jar actually stopped.
6. Repeat Steps 3-4 for each of the surfaces listed on the Table.
7. Fill in the Table with your results for each race.

Examine your data to look for trends and record your observations in your Newton’s Lawbook. This will prepare you for the questions that follow. For example, determine if one jar always rolled farther than the other. Look to see which jar rolled farthest on a given surface. Try to figure out why you got the results you did for each jar on each surface.

Write the answers to the following questions.

1. Did the results depend on whether the jar was filled with flour/sand versus iron/lead? If so, in what way?
2. Did the results depend on the kind of surface you used? If so, in what way?
3. What can you say about a body’s tendency to maintain its status quo – its inertia?

Lesson 2

Newton's First Law:

What does it mean in real world terms?