newtons first law

laws of the park newtons first law

If you understand how a skateboard starts and stops, then you already know something about Newtons first law of motion. This law was developed by English scientist Isaac Newton around 1700. Newton was one of the greatest scientists of all time. He developed three laws of motion and the law of gravity, among many other contributions. Newtons first law of motion states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Without an unbalanced force, a moving object will not only keep moving, but its speed and direction will also remain the same. Newtons first law of motion is often called the law of inertia because inertia is the tendency of an object to resist a change in its motion. If an object is already at rest, inertia will keep it at rest. If an object is already in motion, inertia will keep it moving.

changing direction

Coreys friend Jerod likes to skate on the flat banks at Newtons Skate Park. Thats Jerod in the Figure 1.3. As he reaches the top of a bank, he turns his skateboard to go back down. To change direction, he presses down with his heels on one edge of the skateboard. This causes the skateboard to turn in the opposite direction.

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do you get it

Q: How does Nina use Newtons first law to start her skateboard rolling? A: The skateboard wont move unless Nina pushes off from the pavement with one foot. The force she applies when she pushes off is stronger than the force of friction that opposes the skateboards motion. As a result, the force on the skateboard is unbalanced, and the skateboard moves forward. Q: How does Nina use Newtons first law to stop her skateboard? A: Once the skateboard starts moving, it would keep moving at the same speed and in the same direction if not for another unbalanced force. That force is friction between the skateboard and the pavement. The force of friction is unbalanced because Nina is no longer pushing with her foot to keep the skateboard moving. Thats why the skateboard stops. Q: How does Jerod use Newtons first law of motion to change the direction of his skateboard? A: Pressing down on just one side of a skateboard creates an unbalanced force. The unbalanced force causes the skateboard to turn toward the other side. In the picture, Jerod is pressing down with his heels, so the skateboard turns toward his toes.

starting and stopping

Did you ever ride a skateboard? Even if you didnt, you probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. Thats what Coreys friend Nina is doing in this picture 1.1. Do you know how to stop a skateboard once it starts rolling? Look how Ninas friend Laura does it in the Figure the skateboard. Even if Laura didnt try to stop the skateboard, it would stop sooner or later. Thats because theres also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact.

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instructional diagrams

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questions

without an unbalanced force acting on it, a moving object will

a) keep moving.

b) maintain a constant speed.

c) keep going in the same direction.

-->  d) all of the above

if you dont try to stop a rolling skateboard, it will keep moving forever.

a. true

-->  b. false

pressing down on one side of a skateboard causes it to turn toward the opposite side.

-->  a. true

b. false

if you run into a curb on a skateboard, you will fall forward off your skateboard because there is an unbalanced force applied to your body.

a. true

-->  b. false

diagram questions

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