Third-class levers have an input force, a fulcrum and an output force. The placement of the fulcrum, input and output forces of the lever determines its type.
A lever is a simple machine where a rigid arm is attached around a fixed point. This fixed point is called a fulcrum. The force that is put on a lever is called an input force. This input force creates an output force. A terrific example of a lever is a seesaw. When one child sits down on one end of the seesaw, he or she exerts an input force that is exerted on the other side when the other child is raised from the ground. This back and forth motion between the input and output force is the very fun of the seesaw. A seesaw is considered a first-class lever since its fulcrum is between input and output forces. The fulcrum is at the end while the output force follows then the input force in second-class levers. Wheelbarrows are a type of a second-class lever. The wheel is the fulcrum while the person holding the wheelbarrow exerts the input force. The things inside the wheelbarrow need an output force in order to be lifted. The input force is in the middle of the output force and the fulcrum for third-class levers. Here are some examples of third-class levers.
An Elbow Lifting a Bowling Ball Taking part in bowling is always fun. If people pay close attention, they will see physics in play. A person's elbow acts as the fulcrum in this example. It produces speed in a range of motion to lift a bowling ball. It requires a great amount of force to even move a medium-sized bowling ball. The input force is the muscles that are attached to the elbow. The output force, in this example, is the ball as it is being lifted.
Snow Shovel When there is a heavy snowstorm, snow paths must be shoveled so that maneuvering around through the snow is possible. When someone is shoveling snow, his or her hand attached to the middle of the shovel and is lifting the snow is considered the input force. The snow on the shovel is receiving the output force while the hand that is attached to the handle of the shovel is considered the fulcrum. This is the axis where the lifting of the snow occurs.
Baseball Bat Many people enjoy going to a baseball game yet never realizing that physics examples are being demonstrated constantly while they are watching the game. When a baseball is hit, the action of the hit is considered the output force. This output force is provided by the far arm that swings towards the ball, which is considered the input force. The fulcrum, in this example, is the new arm that holds the bottom portion of the bat.
Canoe Oars Gliding through the water with canoe oars is a necessity to get from point A to point B. The movement of the oars through the water is an example of an output force. When the person pulls on the middle of the oar, this creates an input force. The hand that holds the other part of the oar is considered the fulcrum. Since the canoe oars are tipping back and forth through the water, the fulcrum changes continuously from one hand to the other.