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First-Year Engineering Program
Lab Safety Policies• Don’t stand on lab
chairs• Don’t sit or stand on lab
tables• No dangling jewelry or
loose clothes.• NO open toed shoes.• Be careful with sharp
corners.• Recall location of phone
and first-aid kit.• Report ALL injuries
1
First-Year Engineering Program
Overview of Labs
2
Lab 1 Introduction to Roller Coaster Design
Lab 2 Roller Coaster Energy Losses
Lab 3 Roller Coaster Circuits with Circuit Prototyping
Lab 4 Roller Coaster Speed Sensor Calibration
Lab 5 RC Building Session #1
Lab 6 RC Building Session #2
Lab 7 RC Building Session #3
Lab 8 RC Final Construction - Preliminary Testing of Design
Lab 9 RC Final Testing of Design
Lab 10 RC Oral Presentations
First-Year Engineering Program
Recap of previous lab Law of Conservation of Energy
• Energy can neither be created nor destroyed• Energy can transfer from one form to another
Examples of Energy Losses are the following:• Resistive forces, such as friction and air
resistance• Act on a body in motion and cause energy to
be transferred to unwanted forms (i.e. heat).For the roller coaster ball,
4
+ +
= + + + “Energy Losses”1PE 1TKE 1RKE
2PE 2TKE 2RKE
First-Year Engineering Program
Recap of physics reading moduleFriction is a process that results in a
force that opposes an action. • Static Friction (acts to prevent motion)• Kinetic Friction (exists between moving
surfaces)• Sliding Friction (due to sliding action of the
object)• Rolling Friction (due to rolling action of the
object)Friction causes your ball to lose energy
as it traverses along the track. 5
First-Year Engineering Program
Slippage results from a steep angle causing the ball to slide rather than roll.• Sliding friction is generally greater than rolling
friction.Curved Motion
• Critical velocities:• At the top of a loop:
• At the top of a bump:
• Bank angle creates the centripetal force needed to keep the ball on the track. 6
Recap of physics reading module
gRv
gRv
First-Year Engineering Program
Lets put it all together! Initial energy (i.e. potential energy) is
imparted to the ball by raising it to a certain height ‘h’ • Part of the initial energy will be used:
• To move the ball from the beginning to the end of the roller coaster through loops, bumps, inclined planes and straight sections
• To overcome all energy losses along the track (including friction)
How much energy will be lost due to rolling friction?• The value of µR (coefficient of rolling friction) can be
calculated• This will give you a good estimate as long as the ball is
not sliding along the track
7
First-Year Engineering Program
Agenda• Friction (one form of energy loss)• Slippage• Curved motion (and why it needs to be
handled separately)• Additional (unaccounted for) energy losses• In-Lab activities:
• Experiments to calculate Static/Rolling friction coefficients
• Experiments to calculate average G-force
8
First-Year Engineering Program
Roller Coaster Energy Analysis Spreadsheet
• You will be using a RC Energy Analysis Spreadsheet to model most, but not all of the energy losses that your coaster will experience.
• This Excel spreadsheet allows for• Vertical loops/curves• Bumps• Horizontal loops/curves• Relatively straight sections of track
• Energy losses due to friction, G-forces and air resistance are included. 9
First-Year Engineering Program
Additional Energy Losses• Snap-fit spacing - Too wide a spacing can
cause excessive energy losses through track deformation.
• Structural stability (including track) - An unstable structure can cause energy losses through movements within the structure. Bending of the track can also cause energy losses.
• Differential forces between rails along horizontal curves –The ball will exert a different amount of force on each rail of the track.
10
First-Year Engineering Program
Additional Energy Losses
11
In today's lab• You will gain experience:
• Using the speed sensors • Instrumenting one design feature
• Compare energy losses in coaster to those expected in the RC Energy Analysis Spreadsheet
• One reason for differences:• G-force related losses in horizontal loops
In your final project report you will use this information to discuss where your coaster is losing more energy than shown by this spreadsheet and why.
First-Year Engineering Program
A final consideration: projectile motion
• You need to let your ball fall off the end of your track and land in a box – how far away does the box need to be?
• If the track at the end of the run is horizontal and at a height h, and the ball is at a speed v, then:
g
hv 22distance
12
First-Year Engineering Program
Lab Activities (Part 1)• Lab Apparatus
• Circular Arc (Rolling Friction)• Ramp (Static Friction)
• Group Rotation• Data will be collected at the front table by each
team. • Each team will take turns rotating to the table
and collect data with one ball on a total of three apparatus.
• Each group will be notified when it is their turn to rotate to the front table.
• Each group should record their data on the printed worksheet at the front table and on the computer at the instructor’s station.
13
First-Year Engineering Program
Circular Arc Apparatus - Friction
14
Ball is released at point A.
The type of motion (oscillation, simple harmonic motion) is a way to roll a ball a relatively large distance with a relatively small apparatus.
Ball oscillates for some time and eventually comes to rest –Why?
A
First-Year Engineering Program
Ramp Apparatus - Slippage• In the lab you will determine the value of angle,
β, at which the conjoined balls begin to slide down the ramp.
15
W = mg
motion
β
Body doesn’t slide
Body just begins to slide
W = mg
βNO MOTION
From β you can calculate ΘC, the angle above which you can expect slippage of a single ball on your roller coaster (with increased energy losses). The calculation is in the lab procedures.
First-Year Engineering Program
Vertical Loop Apparatus – G force
16
SP3
SP2
SP1
RUNG 5
RUNG 1
STMP
S1,2,3
Hsp1
Hsp3
Hstmp
Hsp2
For consideration only, you will not be actually using this device in the lab.
First-Year Engineering Program
Vertical Loop Apparatus• If this device were used today, you would
do the following:• Measure the speed of the ball going into the
loop using a speed sensor• Measure the speed of the ball leaving the loop
with another speed sensor. • Calculate the amount of energy lost by the ball
while rolling through the loop.• Compute the energy coefficients for use in the
Roller Coaster Energy Analysis Spreadsheet for losses in curved paths (G – forces). 17
First-Year Engineering Program
Lab Activities (Part 2) This activity will be done at your
table during the entire lab period. Locate your sample build kit, speed
sensors, Arduino board. Build the support structure and
track. Take measurements for four cases. Analyze, graph, and discuss your
results.18
First-Year Engineering Program
Experimental Setup
20
You'll add speed sensors at the beginning and end of the horizontal curve and measure the energy losses for different starting points.
Sensor A
Sensor B
First-Year Engineering Program
Speed Measurement Accuracy
21
Tests of production speed sensors show an accuracy of about +/- 2% when using a correction factor of 1.085. This is with the LED and photo-transistor visually aligned.
Visually confirm that the glued alignment of the two LEDs is correct.If not aligned, errors of up to 10% can occur!
First-Year Engineering Program
Let’s put things together!• Energy losses on straight track:
• Frictional forces• Air resistance
• Additional energy losses:• Snap-fit spacing• Structural stability• Differential forces between rails
• A ball following a curved path:• Involves centripetal force.• Has different frictional losses than when
rolling on straight track. 22