Engineering Mechanics Introduction Download: http://skillcruise.com/academics/mechanical-engineering/engineering-mechanics/

1. IntroductionIntroductionIntroductionIntroduction

2. INTODUCTIONINTODUCTION
OBJECTIVESOBJECTIVES
• Define force
• Classify forces
• Define Kinematics
• Define Kinetics

3. INTRODUCTIONINTRODUCTION
WHAT ARE FORCESWHAT ARE FORCES
• Forces enable us to start moving, stop moving, and change
directions
• We manipulate the forces acting on us to maintain our
balance in stationary positions (e.g. cyclist, diver)
• Simply defined, a force is a push or a pull
• Forces are exerted by objects on other objects

4. INTRODUCTIONINTRODUCTION
WHAT ARE FORCESWHAT ARE FORCES
• Forces come in pairs; the force exerted by one object on another is
matched by an equal but oppositely directed force exerted by the
second object on the first—Action and reaction
• Forces accelerate objects—Start, stop, speed up, slow down, or
change direction
• SI unit is N (Newton)
• 1N force is the force that would accelerate a 1kg mass 1m/s2
• 1N = .225lb
• 1lb = 4.448N

5. INTRODUCTIONINTRODUCTION
WHAT ARE FORCESWHAT ARE FORCES
Describe the force a shot-putter exerts on a shot at the instant shown in Figure
Factors we want to know:
• Size
• Point of application
• Direction (line of action)
• Sense (pushes or pulls along the line of action)
Force is known as a vector
• Mathematical representation of anything described by size or direction

6. INTRODUCTIONINTRODUCTION
WHAT ARE FORCESWHAT ARE FORCES

7. CLASSIFY FORCESCLASSIFY FORCES
INTERNAL FORCESINTERNAL FORCES
• Forces that act within the object or system whose motion is being
investigated
• Muscles pull on tendons, which pull on bones
• At joints, bones push on cartilage
• Tensile forcesTensile forces Pulling forces acting on the ends of an internal
structure
• Compressive forcesCompressive forces Pushing forces acting on the ends of an internal
structure

8. CLASSIFY FORCESCLASSIFY FORCES
INTERNAL FORCESINTERNAL FORCES
• Sometimes the tensile or compressive forces acting on a structure are
greater than the internal forces the structure can withstand—
Structure fails or breaks—Muscle pulls, tendon ruptures, ligament
tears, bone breaks
• Muscles can only produce internal forces—They are incapable of
producing changes in the motion of the body without external forces
• Body is only able to change its motion if it can push or pull against
some external object (e.g. ground reaction force)

9. CLASSIFY FORCESCLASSIFY FORCES
INTERNAL FORCESINTERNAL FORCES

10. CLASSIFY FORCESCLASSIFY FORCES
EXTERNAL FORCESEXTERNAL FORCES
• Forces that act on an object as a result of its interaction with the
environment
• Non-Contact forces:Non-Contact forces: Objects not touching (e.g. gravity, magnetic,
electrical) Gravity is primarily studied in sports biomechanics
• Gravity (g)Gravity (g) accelerates objects downward at 9.81m/s2
no matter
how large or small the object, and any place on earth (ignoring air
resistance)

11. CLASSIFY FORCESCLASSIFY FORCES
EXTERNAL FORCESEXTERNAL FORCES
• Weight—In biomechanics, force of gravity acting on an object—
Don’t confuse with weight as commonly thought of being in lbs from
a bathroom scale
• W = mg
• W = weight (measured in N)
• m = mass (measured in kg)
• g = acceleration due to gravity
• How much do you weigh?

12. CLASSIFY FORCESCLASSIFY FORCES
EXTERNAL FORCESEXTERNAL FORCES
• Contact forces occur between objects in contact with each other
• Objects in contact can be solid or fluid (e.g. air resistance and water
resistance are fluid)
• Forces between solid objects studied primarily in sports
Biomechanics: An athlete and some other object (opponent,
ground, implement)
• To put a shot, an athlete must be holding the shot
• To jump up, an athlete must be in contact with the ground and push
down
• To run forward, an athlete must push backward against ground

13. CLASSIFYCLASSIFY FORCESFORCES
EXTERNAL FORCESEXTERNAL FORCES

14. KINEMATICS and KINETICSKINEMATICS and KINETICS
KINEMATICS:KINEMATICS: It deals with the Bodies in motion without any reference to
the forces which are responsible for the motion.
Description of motionDescription of motion - change in position
•Cars
•sports: baseball, football, soccer, etc.
•world: rotates and revolves
KINETICS:KINETICS: It deals with the Bodies in motion due to application of force.

15. SCALAR QUANTITIES:SCALAR QUANTITIES: A scalar quantity is one which can be completely
specified by it’s magnitude only.
Example:
•Length
•Mass
•Time
•Distance
VECTOR QUANTITIES:VECTOR QUANTITIES: A vector quantity is one which can be completely
specified by it’s magnitude and direction.
Example:
•Displacement
•Velocity ,Acceleration

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