Week 1.2 Flashcards
What are the three basic dimensions in mechanics?
Length, Time, Mass
These dimensions are empirical concepts based on experience and experiment.
What is the basic SI unit for length?
meter (m)
1 m is approximately 3.28 ft or 39 in.
What is the basic SI unit for time?
second (s)
Time orders the sequences in the universe.
What is the basic SI unit of mass?
kilogram (kg)
Mass is the quantity of matter that makes up an object.
What does mass determine in relation to motion?
The effort needed to change the current state of motion of an object.
Is mass the same as weight?
No
Mass is the quantity of matter, while weight is the force of gravity acting on that mass.
What is inertia?
The resistance of an object to changes in its state of motion.
What is the Center of Mass (COM)?
A point in space that moves as if the whole body was concentrated at that point.
How does the position of the COM depend on the object?
It depends on the distribution of the mass of the object.
Where is the COM located in the human body when standing in anatomical position?
55-57% of body height, approximately at the level of the umbilicus.
What is the Center of Gravity (COG)?
The point at which the body can be balanced by a gravitational field.
What is a scalar quantity?
A quantity completely defined by its magnitude.
What are some examples of scalar quantities?
- Time
- Distance
- Energy
- Volume
- Mass
- Work
- Power
- Speed
What is a vector quantity?
A quantity that possesses magnitude and direction.
How do vector quantities add?
According to the Parallelogram Law.
What is the SI unit of force?
Newton (N)
1 N = 1 kg.m/s²
What does force cause in terms of motion?
Changes in the motion of an object, or accelerations.
What is the line of action in relation to force vectors?
An imaginary line that extends along the shaft of the force vector.
What are external forces?
Forces that act on a system of interest due to interaction with the surrounding environment.
What are contact external forces?
Forces resulting from two or more objects in contact with one another.
What is the Universal Law of Gravitation?
Describes the force of attraction between two bodies and defines the concept of weight.
What is the formula for gravitational attraction?
F = G(m1 * m2) / r²
What does weight (W) equal in terms of mass (m) and gravitational acceleration (g)?
W = mg
What is the acceleration due to gravity (g)?
-9.81 m/s²
The negative sign indicates direction toward the center of the earth.
What are internal forces?
Forces that act within a body or segment being assessed.
What happens when external forces exceed internal forces?
The structure fails.
What are internal forces?
Forces that act within a body/segment being assessed
Internal forces help maintain the structure and prevent deformation.
What happens if external forces applied to a segment exceed internal forces?
The structure fails
This indicates the importance of internal forces in maintaining the integrity of the body.
In the context of biomechanics, what is a system of interest?
The whole body or a defined segment of the body
It is the focus of the analysis regarding forces and motion.
What is the significance of the center of mass (COM) in motion?
To change the motion of the whole body COM, external force(s) must act on the body.
The COM is crucial for understanding overall body motion.
What does Newton’s First Law of Motion state?
An object at rest or moving at a constant speed will remain so until acted upon by a non-zero resultant external force.
This law explains inertia and the conditions for changing motion.
What is the mathematical expression for Newton’s First Law of Motion?
v = linear velocity of the object; Σ F = the resultant external force acting on the object
Σ represents the sum of all forces.
What does Newton’s Second Law of Motion describe?
If a non-zero resultant external force acts on an object, the object will accelerate in the direction of that force.
This law relates force, mass, and acceleration.
How is linear acceleration expressed mathematically in Newton’s Second Law?
Σ F = m * a
This shows the relationship between force, mass, and acceleration.
What does Newton’s Third Law of Motion state?
To every action, there is always opposed an equal reaction.
This law emphasizes the interaction between two bodies.
Fill in the blank: If the resultant external force acting on an object is zero, the object will _______.
remain at rest or continue moving at a constant velocity
This is a consequence of Newton’s First Law.
What type of mechanics studies the internal forces within a body?
Deformable body mechanics
This field examines how materials deform under stress.
What is required to change the motion of an object?
The presence of a non-zero net (resultant) external force
This is a critical principle in dynamics.
