Linear and Angular Kinetics

Weight is the measure of your ___ to Earth.

attraction

T or F. A moment is not always required to start, stop, or alter angular motion.

False. A MOMENT IS ALWAYS NECESSARY.

T or F. Inertia is directly proportional to angular velocity.

False. As inertia increases (resistance), angular velocity must decrease - and vice versa. *to decrease inertia, reduce the radius/distribution

T or F. Friction is required to start, stop, or alter motion.

False. Force is required.

T or F. In a squat position, the knee moment arm is greater than the hip moment arm.

False. The perpendicular distance from the axis is greater from the hip, not the knee.

Mass can help indicate how difficult it is to accelerate an object. But masses also ___ one another.

attract - larger masses have larger attractions (like gravity on earth)

For the example of two bats with donuts placed in different spaces, why is it easier to swing the bat with the donut closer to the bottom?

by getting the axis of rotation (handle) and mass (donut) closer together, the resistance to rotation is smaller

The law of inertia states that "If no external forces act on a body then the velocity of the body remains ___"

constant

The equation for inertia is:

inertia= summation of mass times radius squared

T or F. Center of mass has to be located within the body.

False.

There are 3 of Newton's linear Laws of Motion: ___ ___ and ___.

- law of inertia - law of acceleration - law of action-reaction

In regards to somersaulting, if the force acts through the COM, d will = ___ and T will = ___.

0 , 0 which will cause jumping to occur

According to the graph from lecture, the trunk and head contribute ___% to GRF. The legs give __% and the arms give ___% each.

50% - head and trunk 17% - legs 5% each - arms

The constant for gravitational acceleration is ___.

9.81 m/s^2

The equation for the law of acceleration is:

F = m x a - force is a product of mass and acceleration

___ is about how much matter there is in the body.

Mass

The unit for torque is ___.

Newton-meters, Nm

What two equations are there for torque (T)?

T = inertia x angular acceleration (alpha) T = force x moment arm of force (d = distance in meters)

T or F. In regards to somersaulting, if the force acts away from the COM, d will have a magnitude and force will cause a turning motion.

True.

T or F. Moment of inertia is a function of mass and the distribution of that mass.

True.

T or F. Newton's Laws of Motion form the basis for understanding human movement.

True.

T or F. The direction of acceleration follows the path of the force being applied to an object.

True.

The three components of ground reaction force are:

VERTICAL (up), forward-backward, and side to side (medial-lateral)

The equation for weight is:

W = m x g - weight is a product of mass and gravitational force

1 Newton equates to the force needed to change the ___ of a 1 kg mass by 1 m/s^2.

acceleration

Humans are always experiencing forces acting on our bodies, such as ___ and ___.

air resistance and friction

The first angular law states: "if no external moments act on a body, the ____ remains constant"

angular momentum

Angular momentum is a product of:

angular velocity and moment of inertia H = I x omega

The law of acceleration states that "the acceleration of an object is ___ proportional to the force acting on it and is ____ proportional to its mass."

directly, indirectly

Which has a greater influence on resistance to rotation, mass or distribution of mass?

distribution of mass = radius inertia = mass x radius SQUARED

The law of action-reaction states that "for every action, there is an ___ and ___ reaction"

equal and opposite

The third angular law states: bodies exert ___ and ___ moments on each other.

equal and opposite

The center of mass (COM) is the location about which the mass of a body is ___.

evenly distributed

The unit for mass is ___.

kilograms , kg

The units for force are ___.

kilograms per meter per second squared, kgm/s^2 or Newtons, N

The unit for inertia is ___.

kilograms per meter squared , kgm^2

From the example of balls and cylinders rolling down the hill, we learned that the more close the distribution, the smaller the radius which means there will be ___ resistance.

less resistance when mass is more closely distributed = smaller radius = less resistance

The extent to which a segment contributes to ground reaction force depends on which two components?

mass and acceleration of center of mass

The unit for acceleration is ___.

meters per second squared, m/s^2

The unit for weight is ___.

milligrams, mg

When comparing two objects with varying masses, such as two balls, and the acceleration is constant for both, will you need more or less force to move the heavier ball?

more force is required to accelerate the heavier ball

A moment is a turning force that gives ___ to something.

motion

Kinetics are forces that cause ___.

movements

The second angular law states: "the angular acceleration of a body is ___ to the moment causing it."

proportional

Moment of inertia is the ___ of a body to rotation about an axis.

resistance

Ground reaction force is the reaction force provided by the ___ on which movement is performed.

surface

Based on the graph for initial contact/mid-stance, vGRF is ___ and hGRF is ___ to decelerate.

vGRF is upward, because acceleration is increasing hGRF is backward = reaction comes back toward center of mass

Another word for moments is ___.

torques

Based on the graph for mid-stance/toe-off, vGRF is ___ and hGRF is ___ to help propel runner.

vGRF is smaller, because less acceleration possible when being propelled forward hGRF is forward = reaction is coming to the front to help propel you forward