Lecture 8 Flashcards
What is the Law of Action-Reaction?
Whenever two objects interact with each other, they exert forces upon each other.
With the Law of Action-Reaction, why do the forces not cancel each other out?
Because the forces are acting on different objects.
When you are running, why does the reaction force initially decrease?
When you exert force on the ground, the ground is also exerting a force upwards leading to a compression force that minimizes peak force produced to prevent injuries.
Why is there greater friction when an object is at rest?
Due to the coefficient of friction that is larger because there is enough time for the surfaces to interact with each other, where there is not enough time when the object is in movement.
How can you reduce friction?
Reduce the amount of load and therefore the normal force. This can be done by changing the angle at which you are pulling.
What factors effect the amount of frictional force there is?
- Load
- Surface Interaction
- Static vs Dynamic.
What does and does not effect the coefficient of friction?
Does: whether object is stationary or moving.
Does not: Mass of object or surface area
When will an object rotate?
If the line of action of the force passes beside (not through) a rotation axis, then object will rotate.
What is torque?
Ability for a force to create rotation.
What factors the amount of torque produced?
Torque depends on the force and the lever arm- the perpendicular distance from the line of action of the force to the point of rotation.
How does torque relate to the human body?
Muscles generate force but action is to produce a torque about a joint (to initiate or control rotation).
Discuss muscular strength.
- ability to generate toque is related to the strength of the muscle.
- within a muscle, strength varies across joint range of motion.
- Strength = increased with cross-sectional area, longer lever arm.
What is the Law of Inertia (law of angular motion)?
Rotating body will continue in a state of uniform angular motion unless acted upon by an external torque.
What is the Law of Angular Acceleration?
An external torque produces an angular acceleration that is proportional to and in the direction of the torque and inversely proportional to the moment of inertia.
Why does not bending your knees when picking up a box is bad for you?
- Larger gravitational movement arms.
- Larger gravitational torques.
- Need larger muscle tone to counteract and lift box - need more muscle force.
- may increase risk of injury.
