EXSC 350 Chap 3-4

Question 0

Momentum formula

Answer 0

M = mass(velocity)

mass is in kg
velocity is in m/sec

Question 1

Joules formula

Answer 1

J=force(distance)

Force is in N
Distance is in m

Question 2

Linear Kinetics definition

Examples

Importance

Answer 2

Forces that cause motion or are caused by motion

Ex: Gravity, Impact force

Important when studying cause of injury

Question 3

Newton’s 1st Law

Answer 3

(Law of Inertia)

The body continues in its state of Rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

“An object in motion tends to stay in motion unless acted upon by an external force.” Same as an object at rest.

Question 4

Newton’s 2nd Law

Answer 4

(Law of Acceleration)

The 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 the body’s mass.

“When a force acts on an object it will cause the object to accelerate proportional to the force and inversely proportional to the mass.”

It takes more force to move a heavy object than it does to move a light object.

Question 5

Newton’s 3rd Law

Answer 5

(Law of Action-Reaction)

When one body exerts a force on a second, the second body exerts a reaction force that is equal in magnitude and opposite in direction on the first body.

“For every action there is an equal and opposite reaction”

Pushing on an object causes the object to push back against you.

Question 6

Conservation of Momentum

Answer 6

In absence of external forces the total momentum of a given system remains constant.

Question 7

Elastic Collision

Answer 7

Objects in a head on collision bounce off each other. Combined momentum is conserved (remains constant).

M1=M2=(mc)1(before impact=(mv)2(after impact)

Question 8

Inelastic Collision

Answer 8

(Plastic)

Objects in the collision stay together after the collision and move together with the same velocity. Combined momentum is also conserved.

Question 9

Force (F) =

Answer 9

mass(acceleration)

ma

Question 10

Impulse (I) =

Answer 10

Ft (change of M)
(mv)2-(mv)1

Kgm/sec or Ns

If an impulse acts on a system it will change the total momentum of the system.

Question 11

When running, each time your foot hits the ground, ______x your body weight is exerted through your lower extremities?

Answer 11

2-3x

The faster you run the greater are your forces of impact.

Question 12

Factors influencing GRF:

Answer 12

Running Speed
Footwear
Ground surface (concrete is the worst to run on - no give)
Grade of surface (greater forces running downhill)
Downhill running = greater DOMS

Question 13

Newton’s Law of Gravitation

Answer 13

All bodies are attracted to one another with a force proportional to the product of their masses and proportional to the distance between them.

Question 14

Fg (force of gravitational attraction) =

Answer 14

G (m1m2)/d^2

Question 15

Impact

Answer 15

Collision of two bodies in a small amount of time.

Question 16

Perfectly Elastic

Answer 16

Velocities of the two bodies remain equal before and after impact.

Question 17

Perfectly Plastic

Answer 17

At least one body deforms and does not regain its original shape and bodies do not separate.

Question 18

Coefficient of Restitution

Answer 18

A unit less number between 0 and 1 that is used to describe the relative elasticity of an impact.

1 = perfectly elastic

0 = perfectly plasic

Question 19

When two bodies undergo a direct collision, the difference in their velocities immediately after impact is _________ to the difference in their velocities immediately before impact.

Answer 19

Proportional

Question 20

e (coefficient of restitution) =

Answer 20

Square root of Hb/Hd

Hb = bounce height 
Hd = drop height

Question 21

Mechanical work (U) =

Answer 21

Fd force x displacement (distance)

Joules

Question 22

1 Joule =

Answer 22

1 Nm = kgm^2/sec^2

Question 23

Positive Work

Answer 23

Object moved in the SAME direction of the force

Concentric (+)

Question 24

Negative Work

Answer 24

Object moved in opposite direction of force

Eccentric (-)

Question 25

Power =

Answer 25

Rate of mechanic work

= U/t = Fd/t = Fv

Question 26

1 Watt =

Answer 26

1 Joule/sec

Question 27

Mechanical Energy

Answer 27

The capacity of a body to perform work.

3 Types: Kinetic, Potential, Strain

Question 28

Kinetic energy (KE) =

Answer 28

Energy in motion.

= 1/2mv^2

Kgm^2/sec^2 = Joule = Nm

Question 29

Potential Energy (PE) =

Answer 29

Energy due to position (capacity to do work)

Wh (weight) x (height)
Or
Mgh (mass x gravity x height)

Question 30

Strain Energy (SE) =

Answer 30

Energy of Elasticity, stored energy in deformation of an object.
(ex: pole vault, tendons)

SE = 1/2kx^2
k = spring constant (stiffness)
x = deformation distance (length)
Units: Nm or Joules

Question 31

Law of Conservation of Me handicap Energy

Answer 31

When gravity isn’t the only acting external force, a body’s mechanical energy remains constant.

Question 32

Law of Conservation of Mechanical Energy Formula

Answer 32

PE + KE + SE = U
Or
Ei=Ef

Question 33

Kinetic energy possessed at take off (when jumping) is _____ to the potential energy when the person reaches peak heigh in the air.

Answer 33

Equal

Question 34

Principle of Work and Energy

Answer 34

The work of a force is equal to the change in E that it produces in the object acted on.

U = change of KE+change of PE+change of TE (thermal energy)