Key Terms
The most common lever found in the human body
Third Class
Force and Resistance are on the same side, but the Force is closer to the axis/fulcrum
"For every action, there is an equal and opposite reaction."
Newton's law of reaction (3rd law)
This phase of gait cycle makes up ~60% of the cycle in walking
Stance phase
Little leaguers are commonly told to choke up on the bat. Explain the appropriate biomechanical term at play and how this would be an advantage to the batter.
The center seeking force
Centripetal force
F = ma is derived from this law.
Newton's law of acceleration (2nd law)
The deep peroneal nerve innervates the anterior tibialis muscle. In individuals where this nerve has been damaged, they lack appropriate strength/activation of the anterior tibialis. This would result in what is called foot slap and is primarily seen during this phase of gait.
Heel strike into loading response
Ron Weasley is attempting to move a cauldron across the dungeon floor but finds it difficult to move at first, he is relieved to find that once he has it moving he has to work less. Describe, in biomechanical terms, why this situation is occurring.
The maximum static friction is higher than the kinetic friction, meaning maintaining motion against friction is easier than initiating movement.
The maximum amount of friction generated between two static forces
Maximum static friction
Due to this law, it is immensely difficult to acheive a state of complete rest due to the presence of gravity, ground reaction forces, and air resistance.
Newton's Law of inertia (1st law)
A body in at rest stays at rest unless acted upon by an external force.
A common injury occurrence in gait is a strained hamstring. This most often occurs during the mid and terminal swing phases due to excessive eccentric activity of which muscle?
Knee flexors
Han Solo and Luke Skywalker are racing. Han's Millennium Falcon is flying on a 400 m perfectly circular course. Luke's T-65B X-wing is flying on a 200m perfectly circular course. Assuming their velocities are the same, explain which starfighter would have less difficulty exiting the course and why.
Centripetal force is determined by the product of mass and velocity squared, divided by radius. Since their velocities are the same, the starfighter with the smaller radius would have a greater centripetal force present.
The amount of motion a system possesses
Momentum
Ice-skaters and divers routinely manipulate this kinetic principle to increase/decrease their angular velocity and do cool stuff by pulling their arms in or extending their arms.
Moment of inertia
By changing the distribution of mass, they increase/decrease the moment of inertia
During the mid-stance phase, this is the primary rocker present.
Ankle Rocker
Olivia Babcock is known for having a very difficult serve, a top-spin serve. The top spin alters the flight path of the ball, which makes it hard to receive and pass. Explain which force is present and why the direction of the spin matters.
Magnus force. The top-spin creates a higher velocity and low pressure created on the bottom of the ball, which pushes the ball down
The type of force driven by Bernoulli's principle: high velocity = low pressure, low velocity = high pressure.
Lift
This concept involves the simultaneous involvement of potential, kinetic energy, and strain energy.
Conservation of Energy
Individuals who have sustained a stroke often experience knee buckling, which occurs during this phase of the gait cycle, primarily due to a deficiency in which muscles?
Loading response OR mid-stance. Quadriceps/knee extensors
Professional drivers are known to "draft" one another. Please describe the relevant principles at play and how drafting is effective.
Drafting – closely following behind somebody in a fluid protects someone from creating a positive pressure at the head, and then using the pressure differential of the person in front of them, creates a “suction” effect, propelling them forward. This is a manipulation of form drag.