In this unit we use the example of holding a 50 lb weight in the hand to learn more about various forces acting within the body, how they are generated, and how to determine their and direction.
The force in the biceps is trying to lift and rotate the forearm around the elbow joint. The is pulling down on the ball and the forearm, causing rotation in the opposite direction to that caused by the biceps. Our intuition tells us that the muscle tension needs to somehow counteract the of the ball with the forearm acting as a sort of . That’s where we’ll start to solve this example.
We know the ball weighs 50 lbs. If we wanted to include the effect of the of the forearm in our example problem we could look up a typical forearm weight and also look up where the of the forearm is located. Instead let’s take this opportunity to practice making justified . We know that forearms typically weigh only a few pounds, but the ball weight is 50 lbs, so the forearm weight is about an (10x) smaller than the ball weight. Therefore, let’s assume the forearm weight doesn’t matter much and continue solving our biceps force problem only including the weight of the ball, which acts at the of the ball.
- OpenStax University Physics, University Physics Volume 1. OpenStax CNX. Jul 11, 2018 http://firstname.lastname@example.org. ↵
- "Weight, Volume, and Center of Mass of Segments of the Human Body" by Charles E. Clauster, et al, National Technical Information Service, U.S. Department of Commerce ↵
the size or extent of a vector quantity, regardless of direction
the force that is provided by an object in response to being pulled tight by forces acting from opposite ends, typically in reference to a rope, cable or wire
attraction between two objects due to their mass as described by Newton's Universal Law of Gravitation
the force of gravity on on object, typically in reference to the force of gravity caused by Earth or another celestial body
a rigid structure rotating on a pivot and acting on a load, used multiply the effect of an applied effort (force) or enhance the range of motion
a point at which the force of gravity on body or system (weight) may be considered to act. In uniform gravity it is the same as the center of mass.
ignoring some compilation of the in order to simplify the analysis or proceed even though information is lacking
designating which power of 10 (e.g. 1,10,100,100)