CHEM ENG 4052 Lecture Notes - Weighing Scale, Net Force, Statics
22 May 2018
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Biomechanics Lecture #1
- You’re responsible for knowing musculoskletal system from anatomy.
- Number pages used for text will be on top so you can use index as not whole textbook is in it.
- On tests, you will get tested on lab material but on questions very similarly asked in the lab manual to be
handed in >> not on menu or how to get to center of gravity but more conceptual problems >> won’t ask
which button pressed on the computer program.
Lecture:
- Mechanics is the science that deals with objects in a state of rest like constant velocity or resting and no
acceleration, and with dynamics, which involves acceleration.
- Statics involves no acceleration.
- For there to be acceleration, there has to be a net force.
- We deal with equilibrium, which is the first situation where there were equal forces and so you don’t
move.
- If you’re driving at constant speed, there are resistive features like friction of the wheels against the
ground, and air resistance, and if you let go of the accelerator, you’ll eventually come to a stop.
- When you’re accelerating, the force produced by the engine and transmitted to the wheels is exceeding
the force that would otherwise cause you to slow down and is also greater than the force exhibited
before.
- So if you’re driving at 120, the forces that cause you to speed up and the force that’s causing you to slow
down are equal in magnitude.
- We’ll relate this to the body as in muscles causing movement, or dumbbell in the hand resisting
movement >> exact same thing as friction between the wheels and the ground when moving.
- So this is statics >> constant motion.
- Acceleration we won’t really get into.
- F=ma is Newton’s second law, and called the law of acceleration.
- It’s basically the formula for what we just described above.
- The greek symbol just means the sum of >> so sum of forces.
- The forces can be external >> being pushed, or gravity pulling you down.
- Can be internal like from muscles generating force.
- Mass is a resistance to motion >> if you push a fat guy and push a skinny with the same force, who is
likely to move further? The guy that weighs less because the more mass, the less you tend to move.
- If you want to knock a fat guy as far as a skinny guy, you’d have to push the fat guy with more force and
same acceleration.
- Kinematics is the study of motion without reference to forces that cause the motion >> videotaping
someone walking and just watching them >> you wouldn’t know anything about the forces like how
much force you’re applying to the ground, or how much force your muscles are pushing with on the
ground.
- If you videotape someone moving, you can tell how long someone’s stride is, and everytime you take a
step how far you move, how much your knee bends, how much your arms swing >> could tell all of
those things but can’t tell anything about the forces.
- Kinetics discusses the forces that are acting on the body.
- So with kinematics, I can only see you walking without referring to the forces.
- But let’s say as you walk, you stepped on a weighing scale, now you’d know something about forces,
which would be a kinetic approach.
- There are 3 general areas of study when it comes to biomechanics.
- Firstly, describing movement and determining how it is produced >> measuring the movement and
saying something about the forces that acted if we’re looking at the kinematics and kinetics.
- Secondly, assessing how tissues are injured and how injuries can be prevented >> ergonomics.
- Also, if you have a pitcher throwing a curve ball and is starting to get sore, what is causing that
soreness? Damage to the tissues from the repetitive forces.
- Thirdly, determining how performance can be optimized >> how biomechanics and neural control plays
a role in how someone does in their sport.
- In terms of describing how movement is produced, we look at things like human gait (walking), sport
performance, robotics (as a model for how students move to gain more insight).
- Looking at sport performance, FES (functional electrical stimulation) >> used for artificially stimulating
those muscles that would cause muscles if you were paralyzed replacing what the brain would do
because the motor path is destroyed.
- So it may become a viable therapy for spinal cord injuries.
- There are different types of analyses that you’ll do in biomechanics >> qualitative and quantitative >> 2
broad categories of analysis.
- Qualitative is very descriptive >> very relative >> can’t say that someone’s heavy unless you understand
what light means.
- So in qualitative measures you have to mention a reference point otherwise it doesn’t mean anything.
- Quantitative is very numerical >> numbers >> 6 meters, 2 seconds.
- Quantitative you don’t need to compare to anything as walking 1m/s tells you a lot already.
- Qualitative analysis gives you a general description and is used for identifying mechanical principles in
movements >> allows you to get a picture in your mind as to what’s going on.
- Qualitative measurements are used as the first wave of hypothesis generation if we know nothing about
the thing that you want to study.
- Quantitative would be a measured description of skill execution >> walking at 1m/s
- We can use quantitative data for predicting what would happen if conditions change.
- For instance, tall people walk faster than short people because for every stride, they cover more distance
due to their longer legs.
- So there’s a relationship between height and walking speed >> quantitative model.
- So predictions would be, if you know someone’s height, then you can make predictions about how fast
they walk.
- Why do different types of sports lead to different types of injuries, is the movement being performed
through a full range of motion? These are quantitative and qualitative questions that get addressed by
biomechanics.
- Question was asked about what’s the stance phase?
- Swing is about 40% and stance is 50% >> stance is the time that your foot is on the ground, and swing is
the time that your foot is in the air.
- There are 3 planes of motion >> frontal, sagittal, and transverse.
- Looking at the professor would be from the frontal plane.
- If the professor turns around and you see his back, it’s still the frontal plane.
- The sagittal plane is when you’re looking at someone from the side >> doesn’t matte which side.
- The transverse plane is a birds-eye view looking down.
- There are different types of rotations that you’d be able to see dependent upon which plane of motion
you’re looking at.
- In the frontal plane, you’d be able to see raise the arm to the side, and very accurately measure it.
- If I rise arm to the front and you’re looking at me from the frontal plane, you can tell you’re raising your
arm.
- If you want to see shoulder abduction, you’d want to look at the frontal plane because if you look at the
sagittal plane, you can’t get as much information.
- If you want to see shoulder flexion and extension or knee flexion and extension, you’d want to look at
you from the sagittal plane.
- So dependent on what you’re trying to measure, you’ll want a different view.
- If you want to look at head rotation, you’d want transverse plane to look from top down >> birds-eye.
- Any rotations or twisting you need the transverse view (top down) >> transverse plane.
- There are certain activities that we do that occur in mainly one plane.
- Jogging, or riding a bike is in the sagittal plane because that’s how you’d analyze the motions of flexion
and extension of the legs and knees.
- The movements that are in the frontal plane are cartwheel, or abduction and adduction movements.
- The transverse plane motion are the things that are a spin or rotation.
- A lot of our motion is a combination of multiple planes >> a little bit of motion in the sagittal and frontal
plane.
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- Superior is closer to the head (up) and inferior is down >> you can’t say something is just superior
because it’s relative to something else.
- So you have to describe what inferior means.
- So we specify superior as closer to the head and inferior is the opposite.
- Anterior is towards the front >> nose is anterior to the back of the head.
- Medical is towards the midline of the body >> sternum is medial to the shoulder >> closer to the
midline.
- Lateral is the opposite.
- Proximal and distal are talked about often about the limbs.
- Proximal means closer to the trunk, and distal means further away from the trunk >> elbow is distal to
the shoulder but your elbow is proximal to the wrist.
- Superficial is towards the surface of the body and deep is inside the body and so the skin is superficial to
the muscles.
- It’s important to remember that all of these terms are relative >> the shoulder is medial to the elbow but
lateral to your chest.
- Remember that the movements of joints like dorsiflexion are relative!
- Medial rotation is bringing your arm inside your body (remember to be in anatomical position with
palms facing outwards).
- Lateral rotation of the shoulder would consist of bringing your hands out.
- Pronation is palm down, supination is palm up >> think of supination like you’re grabbing a bowl of
soup.
- Supination and pronation is actually a movement of the forearm not the wrist.
- If you bring your arm in front of you, you’re in a flexed posture, and if you bring it behind you, you’re
in an extended posture.
- Remember it’s relative, and you need to define a zero position >> often described as the anatomical
position with palms facing outwards and feet shoulder length apart.
- You don’t have to use it as zero >> many would bring arms to a more natural situation.
- So you can define zero, and what’s become flexed or extended depends on what you define as zero.
