BIOMECHANICS Test 2
Terms
undefined, object
copy deck
 FORCES

 A push or pull
 2 types (internal and external)  INTERNAL FORCES

 Forces that act within the object or system whose motion is being investigated
 In the human body force comes from muscle
 Can't change the body's center of mass
 The body must push or pull while being in contact with something in order to move.  EXTERNAL FORCES

 Forces that act on an object as a result of its interaction with the environment surrounding it
 2 types (noncontact or contact)  NONCONTACT FORCES

 gravity (9.81 m/sec^2)
 Weight is not gravity but the force of gravity acting on an object
W = mg  CONTACT FORCES

 forces between two objects in contact with each other
 Forces that are perpendicular to the surfaces in contact have the strongest force (normal reaction force)
 Friction is parallel to the surfaces in contact. Gravity increases force of friction
F = mu(R)  CENTTER OF GRAVITY

 Males (xiphoid process)
 Females (Lower)  FACTORS THAT DETERMINE HOW HIGH SOMEONE JUMPS

 Weight
 Acceleration of force  SIDES OF A 306090 TRIANGLE

A = 3
B = 4
C = 5  VECTOR
  a physical quantity possessing both magnitude and direction
 VECTOR COMPOSITION

 adding vectors together
 Addition composition of vectors with same direction
 Subtraction composition of vectors with opposite direction
 Resultant results of vector composition  A Woman exerts +25N of force to try to lift a 20N weight off of the floor. What is the Resultant (direction and force)?

+5  left to right diagonal
 Vector addition  A ball weighing 3N is falling to the ground. There is a horizontal wind force of 9N. What is the resultant (direction and force)?

 Vector composition
 9.5N  left to right diagonal  A man pushes a table with a force of 100 N at a 30 degree angle below the horizontal. Calculate the vertical and horizontal forces.

 Vector Resolution
 Vertical 80N
 horizontal 60N
 Resultant 100N 
5 elementary school kids are having a tug of war. They are pulling with the forces
Team A: 200N, 300N, 300N
Team B: 200N, 250N, 200N
What is the resultant force for team A?
Which team is winning? 
150N
Team A is winning  The vertical contact acting under a runner's foot is 1200. The horizontal force of friction is 500N. What is the resultant of the 2 forces?
 1300N
 KINETICS
 Forces that cause motion
 KINEMATICS

 The form, pattern or sequencing of movement with respect to time
 Describes the appearance of motion
 Can be both qualitative and quantitative  QUALITATIVE
  might involve a subjective assessment of the sequencing and timing of the movement of different body parts
 QUANTITATIVE
  can be an objective measurement of a particular joint range of motion
 MOTION
  change in position related to space and time
 LINEAR MOTION

 translation
 all parts of the body or an object move the same distance, in the same direction, at the same time  RECTILINEAR MOTION

 linear motion
 same direction in a straight line  CURVILINEAR

 linear motion
 change in the direction
 a curved line  ANGULAR MOTION

 Movement around an axis
 high bars
 pulleys
 any movement of body  GENERAL MOTION
  combination of linear and angular
 POSITION
  location in space
 DISTANCE

 measured along the path of motion without regard to direction
 usually greater than displacement
 in sports you try to make distance equal to displacement  DISPLACEMENT

 change in location with attention to drection
d = change(y) = y(f)  y(i)  SPEED
  distance covered over time
 VELOCITY

 the change in position (displacement) over time
V = (position 2  position 1)/ (time 2  time 1)  LINEAR ACCELERATION

 the rate of change in linear velocity
a = (V2V1)/ (t2t1)
 if a car increases velocity by 1km/hr each second, acceleration of the car is 1 km/hr/sec
 (+) and () can refer to change in velocity
 zero velocity doesn't man no velocity, it means no change in velocity 
A runner completes 6.5 laps around a 400 m track during a 12 minute (720 sec) run. Calculate:
1. distance the runner covered
2. runner's displacement at the end
3. runner's average speed
4. runner's average velocity
5. runner's a 
1. 400(6.5) = 2600 m
2. not enough info (160 m between start and finish)
3. 3.61 m/s
4. .22 m/s
5. 4.6 minutes/kilometer  PACE
  time in minutes divided by distance in kilometers
 POSITIVE ACCELERATION

 indicates that a body in motion is speeding up
 sprinter leaving the blocks  NEGATIVE ACCELERATION

 indicates that a body in motion is slowing down
 baseball player sliding into a base  A soccer ball is rolling down a field at t = 0, the ball has an instantaneous velocity of 4 m/s. If the acceleration of the ball is constant at 0.3 m/s^2, how long will it take the ball to come to a complete stop?
 13.33 seconds
 A ball rolls with an acceleration of o.5 m/sec^2. If it stops after 7 seconds, what was the initial speed?
 3.5 m/s
 PROJECTILES

 are affected by vertical and horizontal forces
 kicking a soccer ball
 long jump
 shot put
 shooting a basketball  LAW OF INERTIA

 a body will maintain a state of rest or constant velocity unless acted on by an external force that changes the state
 once moving at a steady speed in a straight line it will continue moving at a steady speed in a straight line (object moving in space)
 An object at rest will reamin at rest if the net external force acting on it is equal to zero (headrests)
 iceskating push off and eventually slow down because of gravity  LAW OF ACCELERATION

 a force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to th ebody's mass
 it accelerates in the direction you push it in
 if you push twice as hard, it accelerates twice as much
 if it gets twice the mass it accelerates hald as much
F = ma
 If you kick a soccer ball twice as hard it accelerates twice as much  An object has a mass of 15.82 kg and an acceleration of 19.41 m/s/s. What is the force on the object?
 F = 15.82 kg (19.41 m/s/s) = 307.1 N
 An object with a mass of 12.17 kg experiences a force of 10.00 N. What is the acceleration of the object?

10 N = (12.17 kg)a
a = 0.822 m/s/s  An object with a force of 15.08 N on it is accelerating at 10.88 m/s/s. What is the mass of the object?
 1.386 Kg
 IMPULSE
  average force times the duration of application of the force
 MOMENTUM

 mass times velocity
 in sports the mass doesn't change, so a change in momentum is caused by a change in velocity  LAW OF REACTION

 For every action there is an equal and opposite reaction
 if you push on it, it pushes on you
 Running the force exerted on the floor is equal and opposite to the force from the floor  A 90 kg soccer player collides with a 80 kg player. The first player exerts a force of 450 N on the second player. What is the force exerted by the second player on the first?
 400 N
 Two soccer players collide and stop at the spot of the collision. What do we know about the forces exerted by the players?
  the net forces will be equal and opposite
 Can an object be in motion if no external forces act on it?
 yes
 Can external forces act on an object and not cause acceleration?
 Yes because it will have constant velocity
 When you turn a corner while walking, what forces cause you to change direction? Where are the forces exerted on you?
 Forces are exerted on your feet like friction
 You are standing on the floor. Gravity exerts a force downward. What is the equal but opposite force reacting to gravity?
 The floor exerts a force equal to the force of gravity and your weight
 NEWTON's LAW OF UNIVERSAL GRAVITATION

 the force of gravity is between two objects is directly proportional to the masses of the objects and inversely proportional the distance between them
 If mass increases than gravity increases
 If distance decreases gravity will increase  EINSTEIN'S LAW OF GENERAL RELATIVITY

 combines special relativity
 interrelates space and time so the speed of light is constant
 predicts that time can pass more slowly if an observer is moving, depending on their relative speed, with Newton's law of Universal Gravitation
E = mc^2 
Maddie is standing still when her dancing partner, Paul, begins to lift her up and throw her into the air. Maddie's mass is 40 kg. Paul exerts and Average vertical force of 500 N for 1 second Maddie during the lift and throwing motion.
A. What is M 
A. a = 500/40 = 12.5 m/s
12.59.8 = 2.7 m/s
B. V(f) = V(i)^2 + 2g(change y)
1.87 m  WORK

 force multiplied by the displacement of the resistance in the direction of the force
W = Fd
 If the body doesn't move because of opposing forces, no work is performed  POSITIVE WORK

 climbing up the stairs
 concentric muscle contraction
 requires more caloric expenditure than negative work
 Walking with crutches has 2 to 3 times more energy expenditure than normal walking even though mechanical work is only 1.3 to 1.5 times greater
 Walking on sand requires 2.1 to 2.6 times more energy expenditure even though mechanical work is 1.6 to 2.5 times.  NEGATIVE WORK

 force applied to slow down an objects motion through a distance
 descending the stairs
 eccentric muscle contraction
 more injuries but it has greater training benefits  COMMON UNIT OF WORK
 1 joule = 1 Nm
 A force of 10 N moves an object 5 m across the floor. What is the work being done on that object?
 50J
 A weight lifter lifts a weight a distance of 1 m to perform 100 Nm,l or 100 Joules of work. How much weight is he lifting?
 100 N
 POWER

 force times the speed with which the force is applied
P = work / change in time
= force X velocity
 seen in weight lifting and shot putting because it has a time factor  UNITS OF POWER
 1 watt = 1 J/sec
 A force of 100 N is applied at a speed of 2 m/sec. Calculate the power output
 200J
 In a vertical jump test, a 60 kg athlete jumps 60 cm, while a 90 kg athlete jumps 45 cm. Assuming both jumps took the same time, which athlete is more powerful
 Athlete #2
 HOW IS POWER HELPFUL IN THE SHOT PUT?po
 The faster you get your hand out the farther the ball will go.
 WHY IS POWER LIFTING A MISNOMER?
 Time is not necessarily a factor
 KINETIC ENERGY

 the energy a body or obect have because of its motion
KE = 1/2(mv^2)
 When a person jumps off a diving board their KE decreases and when they land their potential increases  POTENTIAL ENERGY

 the energy a body or object has because of its position
PE = wt(ht)
 A ball is thrown vertically into the air. As it goes up KE decreases while potential increases, but when it falls back KE increases and potential decreases.  CONSERVATION OF MECHANICAL ENERGY

 When gravity is the only acting external force, a body's mechanical energy remains constant
 Ex: ball thrown vertically  PRINCIPAL OF WORK AND ENERGY

 the work of a force is equal to the change in energy that it produces in the object acted on
 Ex: tennis ball  3 FORMS OF MECHANICAL ENERGY IN HUMAN MOVEMENT

 kinetic energy
 potential energy (gravitational)
 elastic potential energy  EXAMPLES OF AN ELASTIC OBJECT GAINING ELASTIC POTENTIAL ENERGY

 archery
 tennis 
Which ball possesses more kinetic energy?
A. A 10 N ball moving at 2 m/sec
B. A 5 N ball moving at 4 m/sec 
A. 20
B. 40
Th 5 N ball has more KE  How does the sand in the long jump pit cushion the landing of the jumper?
 It gradually reduces the impact force by spreading the energy over a long distance and or time.
 Why is the back swing important in striking a golf ball? Follow through?
 It increases the displacement of your swing. The longer the back swing the longer you have a greater kinetic energy. There is also a greater velocity.
 Why is being taller and long limbed an advantage for baseball pitchers?
 Greater displacement = work = kinetic energy = velocity
 Why is football helmets thick?
  The increase of the area that absorbs energy and the lining deforms energy so that its less of an impact when it reaches your head. It spreads the energy over a longer distance.
 How does and air bag protect you in a car accident?

 exerts negative work
 decreases velocity of your body over time
 spreads deacceleration over a certain amount of time