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Bumper Cars: Newton's Three Laws of Motion
Bumper cars are a great place to see Sir Isaac Newton's three laws of motion in action. Here's how:
Newton's First Law: Every object in motion continues in motion and every object at rest continues to be at rest unless an outside force acts upon it. This is because all objects have inertia - the property of matter that resists changes to the object's motion. Newton found that if a ball is sitting on a table, it will stay sitting there because that is what it "wants" to do. If the ball is set in motion, it will keep traveling in a straight path because, again, that is what it "wants" to do. An object in motion will not stop, slow down, or change its direction unless an outside force acts on it (such as gravity, friction, and air resistance). When you are riding in a bumper car and end up in a collision with another bumper car, you feel a jolt. This is because your body's inertia wants it to keep traveling in the direction it was moving with the car even though your bumper car has now suddenly stopped.
Newton's Second Law: The greater the mass of an object, the harder it is to change its speed. (More force is needed to move it.) You already know this law and practice it in your everyday life. Something that is small, such as a pebble, is much easier to pick up and throw than something that is large and heavy, such as a boulder. When riding in the bumper cars, you may have noticed that people who weigh less tend to get pushed around more than people who weigh more. The more mass (weight) an object has, the more force it takes to move it. And since all the bumper cars usually have the same top velocity, the cars carrying more mass will never travel as far as the cars carrying less mass after a collision.Newton's Third Law: For every action, there is an equal and opposite reaction. If two bumper cars traveling at the same speed and carrying the same amount of weight run into each other, they will bounce off and move an equal distance away from each other. And based on the second law, if there is a difference in the amount of weight being carried in the two cars, the car with less weight will travel farther away from the point of impact than the car carrying more weight.
Click to learn more about Newton's Three Laws of Motion.
Carousel: Centripetal Force
Imagine spinning a ball on a string around you. The ball is traveling in a circular path. But Newton's first law states that an object in motion stays in motion and that motion is in a straight path, not a circular path. Since the ball is traveling in a circular path, an outside force must be acting on the ball - that force is the string. The string is pulling the ball back toward you, acting as the centripetal force.
Centripetal means "center-seeking" and is the force that is acting on the carousel. The platform upon which the horses and people are riding is the centripetal force that keeps them traveling in a circular motion just as the string was the centripetal force for the ball. As long as the ride is moving slowly enough, the centripetal force of the platform can keep everyone and everything on board. In theory, if the carousel starts moving really fast, centrifugal force* ("center-fearing") takes over and breaks the hold the platform (centripetal force) had on the riders and the riders would fly off.
*Centrifugal force is actually not a real force. If the centripetal force that pulls an object into the center stops working (e.g. the string breaks), then it is the object's inertia that takes over and sends the object traveling in a straight path. You can test this outside by spinning a ball around you and letting go of the string. If centrifugal force was a real force, the ball would move straight away from the center at the point where the string was let go. But it doesn't. Instead, the ball follows its path of inertia and moves in a straight path that is tangent to the circular path.
Free Fall: Potential Energy, Kinetic Energy, and Gravity
In free fall rides, motors are used to take the car and the passengers to the top of a tower, building potential energy as they reach the top. Potential energy is stored energy and has the capability to become working energy. When the car is released, the potential energy is turned into kinetic energy (the energy of motion) as gravity pulls the car and passengers back down to the earth. However, no matter what an object weighs, all objects fall at the same rate*. So both you and the car are falling at the same speed, giving you the feeling of weightlessness.
Now you may be "fooled" into thinking that the car is falling faster than it normally would if gravity was the only acting force (i.e. the ride makers are using motors to make the car fall faster). After all, you did see and feel yourself being pressed up against the bars and straps holding you in as soon as the car dropped. But remember that your body has inertia and wants to stay at rest, as does the car you are sitting in. The mechanism suspending the car at the top of the tower is holding the car, not you. The car is holding you. So when the mechanism that is suspending the car lets go, there is a slight delay of your body falling with the car because your body's inertia wants to keep it at rest. If the same mechanism dropped you and the car at the same time, there would be no delay of your body falling in comparison with the car.
*Although all objects do fall at the same rate no matter what their weight or size, some objects are more likely to be affected by air resistance than other objects. Because of their spherical shape, balls allow air to easily move past them, with little air resistance to slow them down. Feathers and parachutes are shaped to capture the air as they fall to the ground, effectively slowing them down. In a vacuum, all objects always fall at the same speed since there is no effect of air resistance.
Roller Coaster: Putting It All Together
Roller coasters are the perfect place to see all these laws, forces, and energies at work! Roller coasters are not powered by motors the entire way along the ride. In fact, most roller coasters are only pulled up to the top of the first hill - the highest point of the entire ride. Its entire trip relies solely on the potential energy it has gained by its position at the top of this hill. The higher a roller coaster climbs a hill, the greater a distance there is for gravity to pull it down. When the roller coaster comes down the hill, its potential energy is converted into kinetic energy. When the coaster moves down a hill and starts its way up a new hill, the kinetic energy changes back to potential energy until it is released again when the coaster travels down the hill it just climbed. To see how potential and kinetic energy are built up and released, click here.
Gravity and inertia are big players when it comes to how you experience the ride. The force of gravity is measured in g-forces. Most of the time, you are experiencing 1 g, the normal force gravity exerts on you. However, motion can change how you experience the force of gravity. When the cars are traveling up the hills, you feel heavier because your inertia wants you to stay behind and more g-forces are exerted on you. So, if a ride states that it exerts 3 g-forces, then you will feel like you weigh 3 times more than you really do while riding on the ride. Alternatively, when the car travels down the hills, you feel weightless because you are falling with the car and are experiencing 0 g-forces.
When loops and twists are built in the track, the track becomes the centripetal force that keeps the cars and passengers moving in a circular motion. The inertia of the passengers, which wants them to travel in a straight line, makes the passengers feel like they are being "pressed" into their seats while traveling through the loop. When a coaster goes up a loop or hill, it must come down, because for every action, there is an equal and opposite reaction. And if there is not enough force or speed to overcome its mass, a roller coaster cannot make its way through the entire course of its track.
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