https://www.surveymonkey.com/s/D9XPVPS
This is the program assessment survey.
A separate course survey will be administered in class today.
Thanks for a great year, physics phriends!
- sean
Thursday, June 6, 2013
Thursday, May 30, 2013
Real rocket data
For typical rocket with A engine:
Apogee height 57 m
Top speed 34 m/s
Thrust time 0.5 sec
Peak acc 22 g's
Average acc 7.1 g's
Time to coast after burn out until apogee 3.7 sec
Descent rate 5 m/s
Total time of flight 14 sec
You can get approximate values for b and c engines by doubling and tripling these numbers.
Apogee height 57 m
Top speed 34 m/s
Thrust time 0.5 sec
Peak acc 22 g's
Average acc 7.1 g's
Time to coast after burn out until apogee 3.7 sec
Descent rate 5 m/s
Total time of flight 14 sec
You can get approximate values for b and c engines by doubling and tripling these numbers.
Thursday, May 23, 2013
hw for Tuesday
Review all the recent material in preparation for the take-home test:
1. One dimension motion
2. Projectile motion
3. River problems
4. Newton's laws and applications of F = ma
You are permitted to use your notes on the take-home test. I'll give it to you on Tuesday and it will be due Thursday.
1. One dimension motion
2. Projectile motion
3. River problems
4. Newton's laws and applications of F = ma
You are permitted to use your notes on the take-home test. I'll give it to you on Tuesday and it will be due Thursday.
Wednesday, May 22, 2013
Rocket stuff, if you're looking ahead.
Rocket
calculations, if you're working ahead.
Rocket Lab
In this
lab, you will determine the following information about your rocket flight:
Maximum
speed
Maximum
height
Time of
flight
1. Before the flight, record
the mass (in kg) of your rocket. The scale will give it to you in grams – convert
to kg. The rocket should have everything inside of it: wadding,
engine, parachute.
2. Record the type of engine
being used.
3. The average thrust
(Force, F) is the first number (probably 8 or 6) in the above engine type. This
number is in newtons. Record here:
4. Also record the estimated
height (in m), using an altimeter or trigonometry.
(WE WILL DO THIS ON LAUNCH DAY.)
(WE WILL DO THIS ON LAUNCH DAY.)
5. Determine the post-flight
mass. Subtract the following numbers from your pre-launch mass. If the engine is different, ask Sean
A8-3
engine (3.12 g = 0.00312 kg). B6-4 engine (6.24 g = 0.00624 kg)
6. Now find the average mass
(between pre and post launch masses).
7. Calculate the average
acceleration of the rocket during its
thrust period.
8. The time of thrust is
known - it is set by the amount of propellant in the engine. A8-3 (0.5
sec). B6-4 (0.8 sec). See Sean if engine is different.
9. Find the "burnout
speed" of the rocket, using an equation of motion.
10. Determine the height to
which the rocket has climbed by this point.
11. Now, consider the burnout
speed as the (new) initial speed and find the height to which the rocket will continue to climb until it
reaches apogee.
12. Find the total height
(theoretically) achieved.
13. Compare this to the estimated height from launch day. See 4 above.
14. What is the discrepancy between the estimated height (5 above) and the calculated height (13 above). Why are the numbers different? Discuss.
15. Draw a labeled picture that represents the
flight of your rocket.
Tuesday, May 21, 2013
Newton HW
1. Consider a 0.05 kg model rocket.
a. If it has an engine attached that provides 6-N of thrust, what is the rocket's acceleration?
b. If the thrust time is 0.5 seconds, what is the final "burn out" velocity?
c. What will happen after "burn out"?
2. These questions are about mass and weight (the force due to gravity)?
a. What exactly is the difference between mass and weight?
b. What is the weight of a 65 kg woman?
c. How do weight and mass change/compare on the Moon?
3. Imagine standing on a scale in an elevator.
a. How would the scale reading change if you were moving UP with a constant velocity?
b. How would the scale reading change if you were moving DOWN with a constant velocity?
c. How would the scale reading change if you were accelerating up with a constant acceleration?
d. How would the scale reading change if you were accelerating down with a constant acceleration?
e. You have a mass of 80 kg. If were in a moving elevator, accelerating UP at 1 m/s ^2, what would the scale read?
f. What would the scale read if you were in a freely-falling elevator?
4. Give an example of Newton's 3rd law in action.
5. Why do all objects fall toward the Earth with the same acceleration (in the absence of air resistance)? Answer this question in light of Newton's 2nd law.
a. If it has an engine attached that provides 6-N of thrust, what is the rocket's acceleration?
b. If the thrust time is 0.5 seconds, what is the final "burn out" velocity?
c. What will happen after "burn out"?
2. These questions are about mass and weight (the force due to gravity)?
a. What exactly is the difference between mass and weight?
b. What is the weight of a 65 kg woman?
c. How do weight and mass change/compare on the Moon?
3. Imagine standing on a scale in an elevator.
a. How would the scale reading change if you were moving UP with a constant velocity?
b. How would the scale reading change if you were moving DOWN with a constant velocity?
c. How would the scale reading change if you were accelerating up with a constant acceleration?
d. How would the scale reading change if you were accelerating down with a constant acceleration?
e. You have a mass of 80 kg. If were in a moving elevator, accelerating UP at 1 m/s ^2, what would the scale read?
f. What would the scale read if you were in a freely-falling elevator?
4. Give an example of Newton's 3rd law in action.
5. Why do all objects fall toward the Earth with the same acceleration (in the absence of air resistance)? Answer this question in light of Newton's 2nd law.
Newton's Laws redux.
1. Newton's First Law (Inertia)
An object will keep doing what it is doing, unless there is a reason for it to do otherwise.
That means, it will stay at rest OR it will keep moving (at a constant velocity) unless acted on by an unbalanced force.
2. Newton's Second Law
An unbalanced force (F) causes an object to accelerate (a).
That means, if you apply a force to an object (and the force is unbalanced - greater than any resisting forces), the object will accelerate.
Symbolically:
The Force (F) on a mass (m) produces acceleration (a), predicted by the above equation. In detail:
Greater F means greater a
If the Force is kept constant, but the mass is increased, the acceleration will be smaller:
a = F/m
That's an inverse relationship.
There is a new unit for Force - since Force = mass times acceleration, the units are:
kg m/s^2
We give this a new name, the newton (N). It's about 0.22 lb.
3. Newton's 3rd Law
To every action there is opposed an equal reaction. Forces always exist in pairs. Examples:
You move forward by pushing backward on the Earth - the Earth pushes YOU forward.
A rocket engine pushes hot gases out of one end - the gases push the rocket forward.
If you fire a rifle or pistol, the firearm "kicks" back on you.
Since the two objects experience the same force:
m A = M a
That's a little tricky to convey in letters but, the larger object (M) will experience the smaller acceleration (a) and the smaller object (m) will have a larger acceleration (A).
An object will keep doing what it is doing, unless there is a reason for it to do otherwise.
That means, it will stay at rest OR it will keep moving (at a constant velocity) unless acted on by an unbalanced force.
2. Newton's Second Law
An unbalanced force (F) causes an object to accelerate (a).
That means, if you apply a force to an object (and the force is unbalanced - greater than any resisting forces), the object will accelerate.
Symbolically:
F = m a
The Force (F) on a mass (m) produces acceleration (a), predicted by the above equation. In detail:
Greater F means greater a
If the Force is kept constant, but the mass is increased, the acceleration will be smaller:
a = F/m
That's an inverse relationship.
There is a new unit for Force - since Force = mass times acceleration, the units are:
kg m/s^2
We give this a new name, the newton (N). It's about 0.22 lb.
3. Newton's 3rd Law
To every action there is opposed an equal reaction. Forces always exist in pairs. Examples:
You move forward by pushing backward on the Earth - the Earth pushes YOU forward.
A rocket engine pushes hot gases out of one end - the gases push the rocket forward.
If you fire a rifle or pistol, the firearm "kicks" back on you.
Since the two objects experience the same force:
m A = M a
That's a little tricky to convey in letters but, the larger object (M) will experience the smaller acceleration (a) and the smaller object (m) will have a larger acceleration (A).
Newton's Laws
Newton and his laws of motion.
Newton, Philosophiae naturalis principia mathematica (1687) Translated by Andrew Motte (1729)
Lex. I. Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare.
Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.
Projectiles persevere in their motions, so far as they are not retarded by the resistance of the air, or impelled downwards by the force of gravity. A top, whose parts by their cohesion are perpetually drawn aside from rectilinear motions, does not cease its rotation, otherwise than as it is retarded by the air. The greater bodies of the planets and comets, meeting with less resistance in more free spaces, preserve their motions both progressive and circular for a much longer time.
Lex. II. Mutationem motus proportionalem esse vi motrici impressae, & fieri secundum lineam rectam qua vis illa imprimitur.
The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.
If any force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both.
Lex. III. Actioni contrariam semper & aequalem esse reactionent: sive corporum duorum actiones in se mutuo semper esse aequales & in partes contrarias dirigi.
To every action there is always opposed an equal reaction; or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.
Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone: for the distended rope, by the same endeavour to relax or unbend itself, will draw the horse as much towards the stone as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other.
Lex. I. Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare.
Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.
Projectiles persevere in their motions, so far as they are not retarded by the resistance of the air, or impelled downwards by the force of gravity. A top, whose parts by their cohesion are perpetually drawn aside from rectilinear motions, does not cease its rotation, otherwise than as it is retarded by the air. The greater bodies of the planets and comets, meeting with less resistance in more free spaces, preserve their motions both progressive and circular for a much longer time.
Lex. II. Mutationem motus proportionalem esse vi motrici impressae, & fieri secundum lineam rectam qua vis illa imprimitur.
The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.
If any force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both.
Lex. III. Actioni contrariam semper & aequalem esse reactionent: sive corporum duorum actiones in se mutuo semper esse aequales & in partes contrarias dirigi.
To every action there is always opposed an equal reaction; or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.
Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone: for the distended rope, by the same endeavour to relax or unbend itself, will draw the horse as much towards the stone as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other.
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