1D FORCE EQUILIBRIUM DIAGRAM
Choose a 1D scenario where a person or animal is touching at least two surfaces and is not moving.
1. Either sketch the person or animal in the scenario or find a photo. State what the scenario is what the person/animal is doing, if the scenario may not be clear to everyone.
2. State or otherwise indicate your choice of system
3. Identify and indicate the non-negligible interactions between the system and its environment by drawing force vectors on the sketch or photo, being clear about the direction of the vectors and the position of the tail of the vectors.
a. Draw Weight vector (on your sketch or photo) acting on the system to represent the gravitational attraction between the mass of the system and the mass of the earth.
i. This is the only mass-mass interaction you will need to include, as all the other mass-mass interactions are much weaker.
ii. Draw the tail of the weight vector at the center of mass of the system.i
ii. Label the weight vector.
iv. You need not draw the interaction partner of the weight, as your picture will likely not have the center of the earth in it.
b. Optional: Identify the surfaces of contact between the system and the earth by drawing a line at each surface or point of contact between the system and its environment (what is it touching?).
i. We will consider the system and its environment to be neutral, so the only charge-charge interactions to consider are the repulsions that occur at the points of contact between the system and its environment.
c. Draw interaction force pair vectors (on your sketch or photo) to represent the surface-surface or contact-contact interactions between the system and its environment.
i. These should be equal in size and opposite in direction.
ii. Draw the tail of the vectors acting at the point of contact.
iii. Label each force vector.
4. Distinguish which of the interaction forces in each force pair is the one that acts on the system vs. the one that acts on the environment. One way to do this is to this is to draw forces acting on the system as a solid line and those acting on the environment as a dotted line.
5. If your system is not moving, forces acting on it must be balanced. Show this by making sure that the length of the force vectors is such that all the up forces balance out the down forces, and left vectors balance out right vectors.
6. Show the balancing relationship algebraically, using F = 0.