October 15 (Monday) Inertia Problem Solving
If you missed today: Einstein Board
1. Reminders: Push That Cart Lab Due Today by end of day
and Balloons and Bottle Lab due this Friday as is the extra credit GNATS on Multiplying
2. Lights Off Learning so review where we are at currently in Physics
3. Start working on the back side problems on the Unit 2 Problem Sheet (leave the last one for Thursday) and we'll give hints for the grocery sack and elevator ones today.
4. Student volunteers doing inertia tricks that Donatello did last week.
5. Teacher demonstrating more inertia tricks.
Lights Off Learning:
With students heads down on arms and eyes closed in a darkened classroom...Mr. K. will say something like this:
"Relax, take a deep breath and let it out, erase a white board in your mind for me to assist you in drawing a permanent image of the Physics going on currently that will be there when you need it in your future....
The Last Unit was on Motion .... There are only two motions in the universe .... namely...... accelerated and nonaccelerated. Accelerated means you are changing your speed (speeding up or slowing down ... or changing direction we'll get to later in the year) so nonacceleration means you are NOT changing your speed (stopped or going the same speed [like 30 MPH or 36,000 MPH]. In the last unit we noticed that to study motion you need to use vocabulary like speed, and acceleration where your average speed is simply the total distance you traveled divided the time it took you to travel it. And your acceleration is simply your final speed minus your initial speed (your change in speed) divided by the time it took you to change your speed. In uniform acceleration you can also get your average velocity by simply averaging like in math...adding your initial vel. and final vel. and dividing by two. Using the top three formulas one can derive two more (one with time and one without time needed to make the fab five formulas) Also in the first unit we noticed that by noticing the slope of a line tangent at a point in a distance/time graph aided you in seeing the instantaneous velocity and the slope in a velocity/time graph the instantaneous acceleration.
Now in Unit 2 on Acceleration ... Newtons first two laws of motion simply say ...
An object at rest will have a mind of its own (like Garfield) and wish to remain at rest...
... and an object in motion (like the hyperbolic velocity Voyager I spacecraft that just left our solar system) will have a mind of its own and wish to stay in motion IN A STRAIGHT LINE unless acted upon by an external net force ....
NEWTON'S 1st LAW is referred to the LAW OF INERTIA because you'll notice from the 2nd law that the more MASS
............................ side note below you may skip .................
(the heavier the object is on Earth ... remembering that everything is weightless in space so to have more inertia in space weight would NOT be the factor but the objects MASS (meaning how much matter ... atoms [electrons, protons, neutrons] make up the object))
............. continued below ...........................
... the more MASS an object has the more inertia thus the more stubborn to stay at rest or in motion in a straight line.
... Ok, so far so good, but now what IF an external net force does act upon this body??? NEWTON'S 2nd LAW
... IF an external net force acts upon this body....the body will accelerate (change its speed or direction) in such a way that this acceleration will be directly related to this net force (more thrust or push or pull ... more acceleration or change in speed) and inversely related to the mass of the body (more massive ... the less acceleration meaning if more massive it will not change its speed or direction as quickly).
... This is why we did the Factors That Affect Acceleration Lab where we took the friction away by using a frictionless cart and noticed the more washers pulling the frictionless cart the more the cart accelerated BUT if we pulled the frictionless cart with the same 10 washers BUT added mass to the cart ... the more mass the cart had, the less the cart accelerated ....
.... Then we did the PUSH THAT TRUCK lab and timed the truck coasting after we stopped pushing (accelerating) the truck to take friction between the tires and the road into account. So to arrive at the net force we had to add three forces together....namely..... the force to accelerate the inertia of the truck (with and without passengers), the force to accelerate our bodies inertia (the mass of our row pushing the truck), and the force to overcome the constant friction of the tires on the road resisting our efforts to push that truck. .... This week you'll investigate the properties of friction (the force resisting motion of two objects in contact both for the better and the worse...like marriage).
In the next Unit 3 we will get real involved with the hard to realize fact that Forces Come in Pairs.
Thus to end this "lights off learning" ... we rethought about Motion in the last unit (fab five, distance/time and velocity/time graphs and how to read them) ... the current unit on Newtons 1st Law of Inertia and 2nd Law of F = ma last week and friction this week .... and look forward to the fact that Forces come in Pairs in the Next Unit on Action ...ReAction.
Now keep your eyes shut as I turn on the lights .... OK, open your eyes slowly and wake up your neighbor gently if they fell asleep...
With students heads down on arms and eyes closed in a darkened classroom...Mr. K. will say something like this:
"Relax, take a deep breath and let it out, erase a white board in your mind for me to assist you in drawing a permanent image of the Physics going on currently that will be there when you need it in your future....
The Last Unit was on Motion .... There are only two motions in the universe .... namely...... accelerated and nonaccelerated. Accelerated means you are changing your speed (speeding up or slowing down ... or changing direction we'll get to later in the year) so nonacceleration means you are NOT changing your speed (stopped or going the same speed [like 30 MPH or 36,000 MPH]. In the last unit we noticed that to study motion you need to use vocabulary like speed, and acceleration where your average speed is simply the total distance you traveled divided the time it took you to travel it. And your acceleration is simply your final speed minus your initial speed (your change in speed) divided by the time it took you to change your speed. In uniform acceleration you can also get your average velocity by simply averaging like in math...adding your initial vel. and final vel. and dividing by two. Using the top three formulas one can derive two more (one with time and one without time needed to make the fab five formulas) Also in the first unit we noticed that by noticing the slope of a line tangent at a point in a distance/time graph aided you in seeing the instantaneous velocity and the slope in a velocity/time graph the instantaneous acceleration.
Now in Unit 2 on Acceleration ... Newtons first two laws of motion simply say ...
An object at rest will have a mind of its own (like Garfield) and wish to remain at rest...
... and an object in motion (like the hyperbolic velocity Voyager I spacecraft that just left our solar system) will have a mind of its own and wish to stay in motion IN A STRAIGHT LINE unless acted upon by an external net force ....
NEWTON'S 1st LAW is referred to the LAW OF INERTIA because you'll notice from the 2nd law that the more MASS
............................ side note below you may skip .................
(the heavier the object is on Earth ... remembering that everything is weightless in space so to have more inertia in space weight would NOT be the factor but the objects MASS (meaning how much matter ... atoms [electrons, protons, neutrons] make up the object))
............. continued below ...........................
... the more MASS an object has the more inertia thus the more stubborn to stay at rest or in motion in a straight line.
... Ok, so far so good, but now what IF an external net force does act upon this body??? NEWTON'S 2nd LAW
... IF an external net force acts upon this body....the body will accelerate (change its speed or direction) in such a way that this acceleration will be directly related to this net force (more thrust or push or pull ... more acceleration or change in speed) and inversely related to the mass of the body (more massive ... the less acceleration meaning if more massive it will not change its speed or direction as quickly).
... This is why we did the Factors That Affect Acceleration Lab where we took the friction away by using a frictionless cart and noticed the more washers pulling the frictionless cart the more the cart accelerated BUT if we pulled the frictionless cart with the same 10 washers BUT added mass to the cart ... the more mass the cart had, the less the cart accelerated ....
.... Then we did the PUSH THAT TRUCK lab and timed the truck coasting after we stopped pushing (accelerating) the truck to take friction between the tires and the road into account. So to arrive at the net force we had to add three forces together....namely..... the force to accelerate the inertia of the truck (with and without passengers), the force to accelerate our bodies inertia (the mass of our row pushing the truck), and the force to overcome the constant friction of the tires on the road resisting our efforts to push that truck. .... This week you'll investigate the properties of friction (the force resisting motion of two objects in contact both for the better and the worse...like marriage).
In the next Unit 3 we will get real involved with the hard to realize fact that Forces Come in Pairs.
Thus to end this "lights off learning" ... we rethought about Motion in the last unit (fab five, distance/time and velocity/time graphs and how to read them) ... the current unit on Newtons 1st Law of Inertia and 2nd Law of F = ma last week and friction this week .... and look forward to the fact that Forces come in Pairs in the Next Unit on Action ...ReAction.
Now keep your eyes shut as I turn on the lights .... OK, open your eyes slowly and wake up your neighbor gently if they fell asleep...
Get out your Problem Sheet for Unit 2 and notice the problem about accelerating a grocery sack as you lift it. I think about this problem every time I lift a heavy paper sack of groceries. I know that if I pick the sack up too quickly ... the handles will break off or the bottom will break out, but if I pick the sack up real slowly the handles and/or the bottom of the paper sack may hold the groceries. So notice that the problem has two parts... if you pick the sack up extra slow the sack still has take the force of the actual weight of the groceries in the sack; but if you accelerate the sack then you have an additional force added to the weight of the contents to deal with [this acceleration of the sack (F = ma)] so the NET FORCE is the sum of the above two forces.
Also note the elevator problem on the back of the Unit 2 Problem Sheet. I actually took a weight scale in the SPASH elevator and watched my weight increase the instant the elevator started accelerating me (moving me from the rest state to the nonrest state) up and then as I was moving at a constant speed my weight went back to normal on the scale. Reversely, when the elevator started taking me back down to 1st floor (negative acceleration, from rest at the top and starting to drop me) the weight scale indicated I weighed less for a brief moment until as I went down at a constant speed the scale read my true weight again. Think, as you solve this problem, what weight reading would you use in this problem...your true weight, the highest weight the scale read, the lowest weight the scale read, or the difference of the real weight and the other weights????
The below youtube video may help you understand Newton's 1st Law of Inertia better...
Did We Actually attempt the below youtube video inertia demonstration in our class?
The below youtube video helps you see more everyday inertia happenings we demonstrated in class.
How about a few of our videos ... Pulling tablecloth from under plates. ENJOY! 2012 videos



