307 Exam 2 Flashcards
If curl is performed fast then what happens with time, velocity, acceleration, and amplitudes on a plot?
Time decreases and velocity doubles and acceleration x4 so the amplitudes are larger (nonlinear)
If curl is performed with longer forearms then what happens with time, velocity, acceleration, and amplitudes on a plot?
No change in time, velocity and acceleration double, there are higher amplitudes because there is a longer distance traveled
If there is an increased mass on the barbell then what happens with time, velocity, acceleration, and amplitudes on a plot?
The amplitudes have a greater distance between them, hills are larger and valleys are lower for the horizontal and we increase the weight constant (W) in the vertical direction; taller hills and bigger valleys around that constant line.
Inverse Dynamics
Start with kinematics, then kinetics (FBD), then what is actually happening in the muscles
Impulse
Vector quantity, area under force vs. time plot
Momentum
Inertia in motion, vector quantity, mass times COM velocity, momentum of an object remains constant unless there is a net non-zero external force or torque.
Newton’s second law relationships
Sum of the forces equals mass (must remain constant) times change in velocity all divided by change in time which also all equals mass times acceleration
Quasi static
Moving so slowly that you can assume acceleration equals zero, smaller hills and shorter valleys.
Biceps curl impulse-momentum relationship
Momentum and net impulse are zero because initial and final velocities are zero. The force of the hand is equal to the weight because time is non zero
Negative net impulse
We have negative net impulse in order to slow down the weight so the force of the hand is less than the weight of the barbell
Horizontal forces of a curl
Force of the hand in the x direction is equal to zero, because there is no weight component in the x direction
Force: Faster curl
Force of the hand is equal to the weight of the barbell. The force in the up phase is positive, down phase is negative, so during the whole rep the net force is zero because they are equal and opposite, initial and final velocities=0
Force: Longer forearms
initial and final velocities=0, force of the hand=Weight of the barbell
Force: Different mass of the barbell
Force of the hand still=weight of the barbell
‘Giving’
Reduce risk of injury because you increase the time so you decrease the force via the impulse momentum relationship
Follow through
The limb has a lot of momentum that you eventually want to stop so you increase the time it takes, decrease the force.
Linear Work and Power are both
Scalar quantities. you multiply vectors using the dot product and get a scalar product. can be positive or negative (scalars). For work you multiply force times displacement. For power you multiply force times velocity
Work is the area under
force vs. displacement curve, independent of time.
Work and object’s energy
positive work=increases energy of object
negative work=decreases energy of object
Polar form of work calculates
Total work done
Cartesian form of work calculates
Work done broken up into horizontal and vertical components
Polar approach for work includes
F and d are magnitudes, dcos(theta)= amount of d in the direction of F, cos(theta) makes the product positive or negative. At a 90 degree angle, no work done. Less than 90 degrees, positive work done. Greater than 90 degrees, negative work done
Tails of F and d
They are tied together, so the arrows are pointing in different directions outward from each other
Cross method of multiplication of vectors gives you
another vector
Power definition
rate of doing work (work/time)
Work is conceptually ______ while Power can be______
Work is conceptually an average value while you can have average and instantaneous power, no instantaneous work
Work of the biceps curl (up phase)
Fx=0 so the whole term Fxdx=0, work is purely positive and equal to the weight of the barbell
Work of the biceps curl (Down phase)
Fx=0 so the whole term Fxdx=0, Fy is positive and equal to the weight of the barbell but dy is negative and when you multiply those together you get negative work
Whole rep of work of biceps curl
Work=0, displacement (d)=0
Faster Curl for work
No change in work because Vf and Vi both =0
Longer forearms: Work
More work because displacement increases in both up and down phases but over whole rep=0
Shorter forearms: work
Less work because displacement decreases in both up and down phases. But over entire rep, work=0
Increase mass of barbell: work
More work because more force
Decrease mass of barbell: work
Less work because less force
How to read Work vs. time plot
How much work is done relative to the beginning of the movement, no instantaneous work
How to get total work
Add together the horizontal and vertical components. in graph form, vertical direction dominates
Faster curl: power
Increase power because you decrease time
Slower curl: power
Decrease power because you increase time
Longer forearms: power
More work because you increase the displacement so you increase power. But over the whole rep then power=0
Shorter forearms: power
Less work because you decrease displacement so decrease power. But over the whole rep, power=0
Increase mass: power
Increased work from increased force so increased power
Decrease mass: power
Decrease work from decreased force so decrease power
Total power plot (power vs. time) forces
Average force in the horizontal=0, Average force in the vertical= weight of bar. vertical direction dominates so the total looks like the vertical plot
Assumption of work
Total work basically =vertical work
Graphing power plots
You look for zero values in work vs. time plot and you drop them down to power vs. time plot
Muscle contractions: work and power
Concentric contractions=positive work and positive power. Force and displacement are positive
Eccentric contractions=negative work and negative power. Force is positive but displacement is negative
Isometric = 0 work and 0 power because no displacement
Muscle Force-Velocity-Power curve
Nonlinear decrease, more muscle force can be produced eccentrically, rep performed slower=more load, more forces. Muscles can’t produce much force when moving quickly. Can get power because you multiply force times time
Linear Energy definition, scalar or vector, and units
Capacity to do/perform work (J=Nm=kg times m(squared)/s). Energy is a scalar value so no direction and can have positive or negative values
Mechanical Energy
Kinetic, gravitational potential, potential strain (deformation)
Net impulse of 1st half of the curl up phase
Positive value
Average vertical force from the hand on the barbell during 1st half of the curl up phase
Greater than the weight of the barbell. (Force of the hand in the vertical direction minus the weight) times time=positive value
Force of the hand in the horizontal direction during the first half of the curl
Zero. mvi and mvf both =zero so (Force of the hand in the x direction) times time=0 since time is nonzero
Work done in the horizontal direction during 1st half of the up phase of a curl
Zero
If you take the pause out of the curl what happens with the forces in the x and y directions?
Fy=still W of the barbell and Fx=0. This changes the acceleration, this will now have a big negative valley in the middle of the plot
Faster Curl: KE
Nonlinear increase since you are increasing the velocity
Longer forearms: KE
Increased velocity for longer forearms so this would also be nonlinear increases
Different mass of the barbell: KE
Linear changes since mass is not squared in the equation: 1/2mv(squared)
Gravitational potential energy faster/slower rep
No change because there is no change in the mass or the displacement of the bar
Longer forearms: PEg
Large PEg since you have a larger height, linear increase
Increased mass of barbell: PEg
linear increase from the increased mass
Non-conservative energy release (Q) is always
POSITIVE
Springs are where?
Externally in exercise equipment like bands and internally in biological materials like tendons and bones
Hooke’s Law
F=-kx, the negative sign is telling us that k is opposite the direction of delta x (direction of displacement) in order to get back down to zero (restoring force, push or pull)
Hooke’s law is similar to
Newton’s 3rd law
Work(spring) is the area under
force vs. displacement curve
F=kx graph
Linear, slope=k
Average force needed to stretch a spring/band is equal to
half of the force, it is equal to half of the force applied
Force to raise and lower an object are both
Equal to the weight
When doing a curl in the horizontal direction, there is no change in
Gravitational Potential energy because there is no height change
Spring Constant Units
N/m (newtons per meter)
Impulse units
kg*m/s
Momentum units
kg m/s, same as impulse
Work Units
Nm or J or (kg m(squared)/s(squared))
Power Units
Watts (W) or J/s or (kg m(squared)/s(cubed))
power= work/time but it also equals
Fxvx+Fyvy for cartesian and Fvcos(theta) for polar
