Chapter 1 - Forces Part1 (Week 1)

Question 1

What is a force?

Answer 1

A push or a pull
- Always comes in pairs: equal and opposite reactions

Question 2

What can a force do to an object?

Answer 2

Forces accelerate or deform objects

• cause objects to start, stop, speed up, slow down, or change direction (acceleration

Question 3

What does rigid-body mechanics say about forces?

Answer 3

Ignores the deformation property of forces

• Forces just accelerate objects if force is unopposed (COME BACK)

Question 4

What is the units of force?

Answer 4

Pound (lb) or SI’s Newton (N)

Question 5

What does 1.0N equal to?

Answer 5

1.0N = (1.0kg)(1.0m/s^2)

Question 6

Which of the following is a vector quantity?

A) Temperature
B) Mass
C) Speed
D) Force

Answer 6

D) Force

A vector quantity has both magnitude and direction

Temperature, mass, and speed are scalar quantities; have magnitude but no direction

Question 7

How do we describe forces?

Answer 7

1. Magnitude; how strong the force is (Usually in N)
2. Direction: the direction in which the force is applied (line of action)

• Point of application (where the force is applied on an object)
• Uses arrows
• Length, shaft, arrowhead, end

Question 8

What are two types of forces in biomechanics?

Answer 8

Internal forces and external forces

Question 9

What are internal forces?

Answer 9

• Forces that act within the object or system whose motion is being investigated
• Comes in pairs (action and reaction
• Body or implements manipulated by person

Question 10

What is an example of an internal force and what do THEY not do for an object?

Answer 10

Example: Muscle force inside your body - biceps contract to lift your forearm (or muscle pulling on bones)

• DO not change motion of the entire object, they act within the object

Question 11

What are external forces?

Answer 11

• Forces that act on an object as a result of its interaction with the environment surrounding it
• Contact forces
• Noncontact forces

Question 12

What are the types of internal forces?

Answer 12

• Compressive (compression)
• Tensile (tension)
• Shear
• Torsion
• 3-point bending

Question 13

What is an example of compressive force?

Answer 13

(COme back)

Question 14

What is an example of tensile force?

Answer 14

(Come back)

Question 15

What is an example of shear force?

Answer 15

(Come back)

Question 16

What is an example of torsion force?

Answer 16

(Come back)

Question 17

What is an example of 3-point bending?

Answer 17

Fracture (come back)

Question 18

“Failure: forces are greater than the internal forces the structure can withstand.”

What does that statement mean?

Answer 18

Structures relay on their internal forces like tension, compression, and shear to resist external forces like weight, or impact

When a structure fails it means the external forces (like heavy load or sudden impact) are too strong. (“forces are greater than the internal forces”)

Question 19

What is noncontact forces?

Answer 19

Objects are not touching each other (gravity)

Question 20

What is an example of noncontact forces? What about biomechanics?

Answer 20

1. Gravitational force
2. Magnetic forces

Gravity -
Example: When you jump, gravity pulls you back down (Compressive force)

Question 21

How is weight (N) measured in terms of noncontact forces?

Answer 21

mass (kg) x gravity

Question 22

What is contact forces?

Answer 22

Object are touching each other

Question 23

How is contact forces broken down into components?

Answer 23

1. Perpendicular (normal
2. Parallel to surfaces in contact (friction)

Question 24

What is a perpendicular component of a contact force? What is an example?

Answer 24

Normal force:
- Acts perpendicular to the surface of contact
- pushes objects apart to

Examples: When you stand on the ground, the ground pushes upward on your feet (normal force)

Question 25

What is a parallel component of contact force? What is an example

Answer 25

Frictional force - Acts parallel to the surfaces in contact (along the surface - It opposes motion (force acts in opposite direction) or the tendency of motion between the two surfaces Example: When you walk, friction between your shoes and the ground stopps you from slipping

Question 26

What is friction?

Answer 26

Line of action parallel to 2 surfaces in contact, opposes motion or sliding between the surfaces

Question 27

What are two examples of dry friction?

Answer 27

Static fiction, dynamic friction

Question 28

What is static friction?

Answer 28

two surfaces not moving relative to each other (limiting friction) - Friction that keeps an object still when a force is trying to move it - Prevents motion until a strong enough force is applies (Like moving an heavy object on a carpet)

Question 29

What is dynamic friction?

Answer 29

Two surfaces are moving relative to each other (sliding or kinetic friction) - It lower than static friction, which is why it's easier to keep somthing moving once it starts

Question 30

Friction Graph -

Answer 30

(Comeback)

Question 31

"The friction force (limiting friction or dynamic friction) is proportional to the normal contact force and acts perpendicular to it". What does this mean?

Answer 31

Friction forces depends on the normal contact force - The more force pushing down, the more friction you get (more static friction)

Question 32

What is the formula of friction force?

Answer 32

μ×Normal force μ (mu) = Coefficient of friction (depends on the material) Normal force = How hard the surfaces are pushed together

Question 33

Why is dry friction?

Answer 33

Dry friction is the resistance to motion that occurs between two solid objects surfaces that are in contact without lubricant Dry friction (static and dynamic) is not affected by the size of the surface area in contact *Whether you press a wide object or a narrow one with the same weight (normal force), friction stays about the same because pressure increases as area decreases and vise versa

Question 34

What is the coefficient of static friction and dynamic friction?

Answer 34

μs=coefficient of static friction μd=coefficient of dynamic friction

Question 35

Fs=μsR in the static friction equation, what happens when you increase or decrease? Example?

Answer 35

If you increase the normal contact force R - You're pushing the surfaces together more frimly - THis increases maximum static friction - The object becomes harder to start moving Example: A box gets even harder to move if you place a heavy bag on top IF you incerease the coefficient of static friction: - You're using grippier surfaces - It also increase maximum static friction

Question 36

What is locomotion?

Answer 36

Means moving from one place to another. In biomechanics, this includes walking, running

Question 37

What does it mean that "locomotion requires frictional forces"

Answer 37

This mean that your body relies on friction to move forward like - - push against the ground with your feet (like sand)