5.12 Vectors and Forces

Question 1

What is a force in biomechanics?

Answer 1

A push or pull that has both magnitude and direction, making it a vector force.

Question 2

What are the two key components of a vector?

Answer 2

Magnitude (size) and direction.

Question 3

What is a scalar quantity?

Answer 3

A measurement with only magnitude and no direction (e.g., 5 miles, 7 vertebrae).

Question 4

How can a vector force be expressed?

Answer 4

Graphically (arrows) or mathematically.

Question 5

What does the tail of a vector arrow represent?

Answer 5

The point of application of the force (e.g., muscle attachment).

Question 6

What does the arrowhead of a vector represent?

Answer 6

The direction of the force.

Question 7

What does the length of a vector arrow represent?

Answer 7

The magnitude of the force.

Question 8

What units are commonly used to measure force?

Answer 8

Newtons (N) or pounds (lb).

Question 9

Which vector directions are considered positive?

Answer 9

Up and to the right.

Question 10

Which vector directions are considered negative?

Answer 10

Down and to the left.

Question 11

What is the resultant force?

Answer 11

The single force representing the combined effects of multiple forces.

Question 12

How are forces in the same direction combined?

Answer 12

By adding their magnitudes.

Question 13

How are forces in opposite directions combined?

Answer 13

By subtracting their magnitudes.

Question 14

How can angled forces be analyzed?

Answer 14

By breaking them into X and Y components.

Question 15

What is the graphical method of combining multiple vectors?

Answer 15

Place the tail of each new vector at the head of the previous one; the resultant vector runs from the tail of the first to the head of the last.

Question 16

What does the resultant vector show?

Answer 16

Both the magnitude and direction of the combined forces.

Question 17

Example: If multiple downward forces act on a leg (leg weight, boot, added weight), how are they combined?

Answer 17

They are all added together since they act in the same direction (downward).

Question 18

If downward leg forces total –19 lbs, what does the negative mean?

Answer 18

It indicates the direction is downward (negative).

Question 19

Example: In cervical traction, if upward force is 25 lbs and head weight is 10 lbs downward, what is the resultant force?

Answer 19

15 lbs upward (25 – 10).

Question 20

Why isn’t the full traction force applied to separate vertebrae?

Answer 20

Part of it offsets the head’s weight; only the force beyond equilibrium produces therapeutic separation.