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Your Body’s Levers
When you think of a lever, you may picture a seesaw structure or a handle, but did you know that you have levers in your body, too? A lever is just something bar shaped that rotates about a fulcrum, which acts as the axis of rotation. A lever acts as a force, which increases velocity and thus acceleration in the direction it is applied. Resistance acts in opposition to the effects of an object’s energy.

The Three Classes of Levers in Your Body and around You
First Class
For this class of lever, the motive force (the applied exertion of effort) and resistive force (force opposing this exertion) are on either side of the fulcrum, which is right in the middle. Tools such as scissors and seesaws are examples of this type of lever. When you flex your muscles, agonistic and antagonistic muscle groups act as the force and resistance, respectively. In your arm, your elbow is the axis of rotation. The axis being midway between the force and the resistance results in greater speed, force, and range of motion.

Second Class
Second class levers have resistance between the axis and the applied force. When you use a nutcracker or wheelbarrow, you are using a second class lever. An example of a second class lever in your body is your foot when you stand up on your toes. The balls of your feet are the axes in this case. Your ankle plantar flexors act as a force against the resistance of the body at tibial articulation. Second class levers result in smoother movements because of less inertia, as well as less force.

Third Class
In third class levers, the force is between the axis and resistance. One example is a person positioning their hands on the middle (force) and the end (axis) of the oar through the water (resistance). The knee acts as a third class lever when your hamstring contracts (force) and your lower leg flexes as a result (resistance). Third class levers lead to higher levels of inertia, meaning they are harder to stop.

As you may have noticed, the relative positions of the axis, exerted force, and resistant force have an impact on factors such as inertia and how smoothly movement occurs. The classes of levers provide different combinations of important mechanisms, each of which is important for a different class of tasks.

Examples of First, Second, and Third Class Levers. First Class, the Fulcrum is below and in the middle of Effort and Load which are above. Second Class, the Load is on top in the middle of Effort and the Fulcrum which is at the right. Third Class, Load is on top at the right, Effort is below in the middle, and the Fulcrum is below to the left.

Describe each class of lever and explain the characteristics of each. (Site 1)