Momentum. Carnival Physics: Midway Games. Two common carnival games, "Break the Plate" and "Knock the Blocks off the Table," require energy (the ability to do work or make changes to the physical world) to win. Where does that energy come from? The energy comes from you, the player. When you throw a ball, you transfer energy to the ball. The amount of kinetic energy, or energy of motion, that the ball has is related to both its mass and its speed. When the ball strikes an object, such as a plate or a block, the impact transfers energy from the ball to the object, exerting a force on the object.
Interestingly, it turns out that the position of the plate plays a big part in determining the amount of force that will act on it. For example, safety airbags in cars extend the duration of the impact between a person and the windshield. Defy Gravity! Centripetal Force. According to Newton's law of inertia, an object already moving will continue to move in a straight line at a constant speed unless acted on by an outside force. Thus, to make an object move in a circular path, an outside force must act on the object. Centripetal force is the force that pushes or pulls an object inward so that it will move in a circular path. The word centripetal means to seek the center. When you whirl a stone tied to a string in a circle, you must constantly pull on the string to keep the stone from flying off in a straight line.
The force the string applies to the object is the centripetal force. Centripetal force operates in other scenarios as well, acting, for example, on a car to make it travel around a curve. In the initial demonstration of this segment from ZOOM, involving a cylindrical container, as the ball rolls around the inside of the cylinder walls, a centripetal force continually redirects it to the center of the cylinder. Welcome to Amusement Park Physics. Newton's Third Law of Motion: Astronauts in Outer Space. One of NASA's first attempts at a "space walk" turned into an exhausting failure for astronaut Gene Cernan. Unlike astronauts who had "walked" in space on previous missions, Cernan had several tasks to accomplish outside the spacecraft. However, every time he attempted to push or turn a valve, he was sent hurtling in the opposite direction, with little control over his trajectory. After many exhausting minutes, his mission outside the capsule was called off, and NASA scientists began trying to figure out what went wrong.
NASA scientists and engineers should probably have predicted that if an astronaut applied force to open or close a valve, the valve would apply the same amount of force to him, but in the opposite direction. After all, nearly 300 years ago, Isaac Newton presented what came to be known as his third law of motion, which says that for every action there is an equal and opposite reaction. Centripetal Force: Pulling Cs and Gs. When an object moves in a circle, which is effectively what a car does when it rounds a bend in the road, the moving object must be pulled or pushed inward toward what's called the center of rotation. It's this force acting toward the center—the centripetal force—that keeps an object moving along a curved path. Centripetal force prevents moving objects from exiting a curve and flying off in a straight line by continuously making them change their direction toward the center of rotation.
Gravity plays an important role in this. On Earth, gravity applies a constant downward force on all objects. For a turning car, the downward force of gravity is matched by the upward force provided by the surface over which the tires roll. So gravity creates the conditions for the friction between the tires and the ground so that, in turn, the ground can provide the push (that is, the centripetal force) needed for the car to turn.
Often, people confuse centripetal force with centrifugal force. Force and Motion. Invisible Forces. There are many different forces acting upon our environment that are invisible to the naked eye. However, just because we can’t see these forces at work doesn't’t mean they don’t exist. The forces around us include gravity, friction and air resistance, to name a few. Sir Isaac Newton defined all of the known forces of nature in the 17th century. He changed our understanding of how the universe works by describing the three laws of motion. Wind, which can be an extremely powerful force, is invisible most of the time.
For one scientist and artist, these forces and motions can be so predictable that they can be manipulated to produce amazing works of art. For more about the laws that affect motions and forces, check out Newton's Third Law of Motion: Astronauts in Outer Space and Galileo: His Experiments.