##### EXS 322 Biomechanics

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1

Force is a ____ or ____

Push or pull

2

Forces are exerted by ____ on other _____

objects on other objects

3

Forces come in ____

pairs; action & reaction

4

The force exerted by one object on another is matched by an ____ but ____ directed force exerted by the ______

equal but oppositely, second object

5

A force is something that ____ or ______ an object

accelerates or deforms

6

In rigid-body mechanics, we ignore ______ and assume that the objects we analyze do not _____

deformations, change shape

7

In rigid-body mechanics, objects do not _____ but they do _____ if the force is _____

deform, accelerate, unopposed

8

Mechanically speaking, something accelerates if it ____, _____, _____, _____, or ______.

starts, stops, speeds up, slows down, or changes direction

9

Our most familiar unit of measurement for force is the ____, but the SI unit of measurement for force is the _____

pound, newton

10

The newton is abbreviated as _____

N

11

One newton of force is defined as the force required to accelerate a

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

1 kg mass 1 m/s^2

12

One newton of force is equal to ____lb of force, or 1lb equals _____ N

.225lb, 4.448 N

13

To fully describe force, you must describe its ___ and ____

size and direction

14

Internal Forces

Internal forces are forces that act within the object or system whose motion is being investigated. Internal forces hold things together when the structure is under tension or compression. Sometimes the tensile or compressive forces acting on the structure are greater than the internal forces of the structure can withstand. When this happens, the structure breaks. Structural failure in the body occurs when muscles pull, tendons rupture, ligaments tear, and bones break.

15

Tensile forces

If pulling forces act on the ends of an internal structure, the structure is under tension and this is tensile force.

16

Compressive Forces

If pushing forces act on the ends of an internal structure, the internal pushing forces are referred to as compressive forces, and the structure is under compression.

17

Internal forces cannot produce any changes in the ____ of the _________

motion of the body's center of mass

18

External Forces

External force are forces that act on an object as a result of its interaction with the environment surrounding it.

19

External forces can be classified as either ____ or ______ forces

contact or non-contact

20

Contact forces occur when ____

objects are teaching each other

21

Non-contact forces occur ___

even if objects are not touching each other.

22

Give an example of non-contact force:

gravitational pull of the earth.

Magnetic forces

electrical forces

23

The force of gravity acting on an object is defined as the _________-

_____ is the force of gravity acting on an object

weight of the object

24

Gravitational acceleration/acceleration due to gravity - abbreviated as g

9.81 m/s^2 or 32.2 ft/s ^2

25

W = mg

Units:

W =

m =

g =

W = weight (newtons

m = mass (kg)

g = acceleration due to gravity = 9.81 m/s^2

26

Objects in contact with each other (contact forces) can be either _____ or ______

solid or fluid

27

Fluid contact forces

air or water resistance

28

Dry friction

Acts between the non-lubricated surfaces of solid objects or rigid bodies in contact and acts parallel to the contact surfaces.

29

Fluid friction

develops between two layers of fluid and occurs when dry surfaces are lubricated.

30

Friction arises as a result of interactions between ______ of the ____ in contact

molecules of the surfaces

31

Static friction

When dry friction acts between two surfaces that are not moving relative to each other.

32

Limiting friction

When describing the maximum amount of friction that develops just before two surfaces begin to slide.

33

Dynamic friction/sliding friction/kinetic friction

When dry friction acts between two surfaces that are moving relative to each other.

34

Dry friction is not affected by the ___ of the _______ in contact

size of the surface area in contact.

35

Friction opposes ______ between the surfaces in contact

relative motion or impending relative motion

36

Friction is proportional to the ________ pushing the ________

normal contact forces, two surfaces together

37

As normal contact forces increase, _________ increase as well

as normal contact forces increase, the frictional forces increase as well.

38

Friction is affected by the _________ in contact

characteristics of the surfaces in contact

39

Greater friction can be developed between _____ and ______ surfaces than between ______ and _______ surfaces

softer and rougher surfaces than between harder and smoother surfaces.

40

______ friction is greater than ______ friction

static friction is greater than dynamic friction

41

Net force

The net force acting on an object is the sum of all the external forces acting on it. The net force is the vector sum of all the external forces. The vector addition of all the external forces acting on an object.

42

Forces are added using the process of _____

43

Resultant force

The result of vector addition of all the external forces acting on an object

44

Colinear forces

Collinear forces are forces that have the same line of action.

45

forces act along the same line and in the same direction

46

Concurrent Forces

If forces do not act along the same line but do act through the same point.

47

Define Biomechanics

the study of forces and their effects on living systems.

48

Sport and exercise biomechanics

the study of forces and their effects on humans in exercise and sport.

49

The ultimate goal of sport and exercise biomechanics is

performance improvement in exercise or sport.

50

Theta represents

the angle

51

Opposite represents

the length of the side of the triangle opposite of the angle theta

52

the length of the side of the triangle adjacent to the angle theta

53

Hypotenuse refers to

the length of the side of the triangle opposite the right angle

54

Sin refers to

Sine

55

Cos refers to

Cosine

56

Tan refers to

Tangent

57

Mnemonic for Sin (theta)

Some of his

58

Mnemonic for Cos (theta)

Children Are Having

59

Mnemonic for Tan (theta)

Trouble Over Algebra

60

If an object is not moving, it is in _____ equilibrium.

static equilibrium

61

In static equilibrium, acceleration is ____, and the sum of all external forces acting on the object is ____.

zero, zero

62

ΣF means?

net external force or vector sum of the external forces

63

The sense of a force or any vector is the

direction in which the arrow of the force or vector points along its line of action.

64

ΣF x

Net horizontal force

Horizontal component of the net external forces

65

ΣF y

Net vertical force

Vertical component of the net external forces.

66

Forces are vector quantities meaning they are

They are vector quantities, so they are described by a size and a direction of action.

67

Internal forces hold things together and cannot cause

Internal forces hold things together and cannot cause changes in the motion of a system.

68

External forces may cause

External forces may cause changes in the motion of the system.

69

The most commonly felt external forces are

The most commonly felt external forces are gravity and contact forces.

70

Friction and the normal reaction force are the

Friction and the normal reaction force are the two components of a contact force.

71

If the net external force acting on an object is zero, the object is

If the net external force acting on an object is zero, the object is standing still or moving in a straight line at constant velocity.

72

If the object is standing still, it is in a state of

If the object is standing still, it is in a state of static equilibrium, and the external forces acting on it are balanced and sum to a net force of zero.

73

If the external forces acting on an object do not balance (i.e., they do not sum to zero), the object is

If the external forces acting on an object do not balance (i.e., they do not sum to zero), the object is not in equilibrium and will change its state of motion.