Biomechanics 01 (forces)

Which of the following define forces?

All of the above

The English unit for Force is the __ and the SI unit is the _

Pound; Newton

What is NOT the correct definition for characterizing a force?

Standard unit = pounds

A Force is a __ quantity, meaning it has both magnitude and direction

Vector

Length of the arrow represents force magnitude

–Arrowhead indicates force sense (direction)

–Shaft of the arrow indicates line of application

–One end of the arrow indicates point of application on the object

True

Which of the following is NOT an assumption in rigid body mechanics?

The body can undergo deformation when external forces are applied, altering its dimensions and shape.

In an internal force, acting within the system, how do the forces affect the object?

Each force affects object part it acts on but does not affect the motion of the body

In an internal force, how would you best describe the forces holding an object together?

Tensile = pulling further apart, Compressive = squeezing together

Which of the following is NOT an example of external force?

Internal force: between parts of the same system

Weight is represented by the equation W = mg

• W = Weight

• m = mass (kg)

• g = gravity (-9.81 m/s²)

—> How is weight defined?

force of gravity acting on an object

Contact Forces are also known as _ forces. Does each force act separately?

Reaction; Yes

Normal contact force

perpendicular to the two objects in contact

Parallel (friction) contact force

parallel to contacting surfaces of two objects; opposes motion

Friction __ between objects in contact, and results from interaction between surface molecules

opposes motion

Static friction

two surfaces not moving on each other

Limiting friction

maximum friction before objects start to slide

Dynamic (Sliding/Kinetic) friction

two surfaces are moving on each other

Friction is proportional to the force (R) pushing the two surfaces together. It is also affected by the characteristics (μ) of the two materials in contact

True

What is the equation to represent friction?

F = μR

Net force is defined as the

sum of all external forces acting on one object

Net force is also defined as __ force. Does it have to account for the direction of each external force?

Resultant; Yes

Colinear Forces identify one direction as positive (+) and the other as negative (-). How do you define them?

One or more external forces with the same line of action

Concurrent Forces

Forces are not colinear but act through the same point

To calculate the resultant (net) force, you do the following sequence

Find net VF —> find net HF —> Use pythagorean theorum to find RF magnitude —> use trig to find RF angle

External forces are always colinear and act only in the horizontal and vertical directions

False

Static Equilibrium

body is not accelerating because there is no change in its motion and forces are in equilibrium