Introduction to Physics of Human Movement

Question 1

Force

Answer 1

A form of energy that
• Causes movement
• Has direction
• Has magnitude
• Point of application

F = m*a, expressed in Newton (N): 1 N = 1 kg * 1 m/sec2

Question 2

Internal Forces

Answer 2

Generated by the muscles

Question 3

External Forces

Answer 3

Applied by a variety of sources, most constant being gravity.

Question 4

Mass

Answer 4

Scalar quantity (without action line or direction), that represents the quantity of matter of an object, in kilograms.

Question 5

Weight

Answer 5

Pull of gravity on the
object’s mass.
Weight = mass * gravity.
It is a force, therefore should be expressed in Newton.

Question 6

Newton’s 1st Law

Answer 6

Law of Inertia

A body remains at the state of rest or remains in uniform motion until an outside force acts on it.

Question 7

Newton’s 2nd Law

Answer 7

Law of Acceleration
The vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = m*a.

Question 8

Newton’s 3rd Law

Answer 8

Law of Reaction
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

Question 9

Mechanical Work

Answer 9

Work = Force * Displacement
Can be positive, negative, or Zero.
Concentric, eccentric, or isometric contractions

Question 10

Power

Answer 10

Power is defined as the rate at which work is done upon an object.
Power = Work / Time or
Power = Force * Velocity

Question 11

Torque

Answer 11

Is a measure of how much a force acting on an object
causes that object to rotate.
Torque equals to the force (F) applied, the length (L) of the lever arm, and the angle
between the force vector and the lever arm.
Torque is greatest when the force is perpendicular to the lever arm.
Torque is zero when the force is parallel to the lever arm.

Question 12

Center of Gravity vs. Center of mass

Answer 12

CoG related to distribution of weight, CoM related to distribution of mass.

Question 13

Center of Gravity

Answer 13

• Changes with motion
• Changes when weight is added to the body
• The lower the center of gravity, the more stable the object
Human CoG located anterior to S2 (in the anatomical position)

Question 14

Line of Gravity

Answer 14

• Runs vertically through CoM
• Used as a point of reference when discussing posture
• Used to determine stability of an object

Question 15

Base of Support

Answer 15

• Simply referred to as the base

* A two-dimensional area between and including an object’s points of contact with the supporting surface

Question 16

Stability

Answer 16

• Simply referred to as the base

* A two-dimensional area between and including an object’s points of contact with the supporting surface