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# BIOMECHANICS Test 2

## Terms

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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 (non-contact or contact)
NON-CONTACT 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 30-60-90 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
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 = (V2-V1)/ (t2-t1)

- 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
- inter-relates 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

12.5-9.8 = 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

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