http://www.ck12.org Chapter 4. Motion and Forces
4.21 Newton’s First Law
- Use skateboarding to explain Newton’s first law of motion.
There’s no doubt from Corey’s face that he loves skateboarding! Corey and his friends visit Newton’s Skate Park
every chance they get. They may not know it, but while they’re having fun on their skateboards, they’re actually
applying science concepts such as forces and motion.
Starting and Stopping
Did you ever ride a skateboard? Even if you didn’t, you probably know that to start a skateboard rolling over a level
surface, you need to push off with one foot against the ground. That’s what Corey’s friend Nina is doing in this
picture 4.39.
Do you know how to stop a skateboard once it starts rolling? Look how Nina’s friend Laura does it in theFigure
4.40. She steps down on the back of the skateboard so it scrapes on the pavement. This creates friction, which stops
the skateboard.
Even if Laura didn’t try to stop the skateboard, it would stop sooner or later. That’s because there’s 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.