Transcript Objective: To calculate the force needed to break an apple

A Calculation of Force Lab
Objective: To calculate the force
needed to break an apple skin,
raw and hard boiled egg shells,
and various produce.
Background
• Objects move in both vertical and
horizontal direction in the shape of a
parabola
• This is because the only force acting on
the object in motion is gravity
• Motion like this behaves in very
predictable ways with regards to time,
velocity and distance
Background
• Remember our practice problems…..
• We can use time to calculate final velocity
– An apple falls from a tree in 0.64s. What was
the velocity of the apple at impact? v=g•t
– V= (9.81m/s2)(0.64s)= 6.3 m/s
Problem
• We are going to calculate the force
required to break the skin of an
apple…as well as other fun stuff.
• First we measure time from the top of
the parabola to the moment it strikes
the ground. Some things can just be
dropped.
• Then we calculate final velocity v=g•t
• This value becomes the initial velocity
in the compression part of the fall
• During compression, the object
experiences the full force of impact as
it rapidly decelerates to a stop.
• If this force is great enough, then the
outer shell fails…splatt
Problem
• http://www.youtube.com/watch?v=90VyvO
hPmA0&p=9A7377D11F047397
• http://www.youtube.com/watch?v=aaim3q
mxhk0&p=9A7377D11F047397
• Once a falling object comes into contact
with the ground is compresses.
• If it falls from a high enough distance or
lands on a hard enough surface the object
will break apart.
V (initial)
The initial velocity is the final
velocity from the previous
calculation. v=g•t
Compression
At impact
Velocity Final =0
Problem
• By using a coefficient for compression
appropriate for grass (0.15). We can use the
change in velocity and calculate acceleration of
compression
• Vf-Vi = acceleration of compression
0.15
• Finally, we use the mass of the object, the
acceleration of compression, and calculate the
Force (F=ma) required to break the apple skin.
Hypothesis
• You have to construct this now. Our
analysis will contain and discuss numbers,
We do not just want to guess numbers.
So, for now just hypothesize the about the
method. We will be measure time of flight.
We will calculate final velocity at impact.
Can we then use this data to calculate the
force required to break the outer surface of
apples, eggs, and produce?
Procedure
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Mass your raw egg, hard boiled egg, apple, and produce from home
using the scales.
Convert this value into kg.
Carefully drop each object from a height that you are sure will NOT break
it.
Then, slowly increase your drop height.
Your must time the free fall of each object carefully.
Record all free fall times and note the time that reflects the fall that broke
the outer surface of the object.
Use time to calculate final velocity for each object v=g•t
Use this final velocity as the initial velocity in the acceleration of compression
calculation. Use 0.15 as coefficient of compression. a(compression)=Vf-Vi = ?
0.15
Use F=ma to calculate force in Newtons (N)
Record all data carefully.
Data
Object
Raw
Egg
Boiled
Egg
Apple
Misc.
Time
(s)
Time
(s) Break
Final
Velocity
(m/s)
Final
velocity
(s)
(m/s)
Data: Outer Surface Fails
Object
Raw egg
Boiled
Egg
Apple
Misc.
Free fall
time
(s)
Final
velocity
(m/s)
Accelera Force
tion
(m/s2)
(N)
V. Analysis
• One graph…for every time of every object
you dropped
• Velocities (y-axis) over time (x-axis)
• This is an acceleration graph
• Show units
• Draw line of best fit through the scatter
plot.
VI. Conclusion
•Did you support or reject your hypothesis?
•Which object required the most force to break?
•The least
•What were some sources of error?
•How would you improve this lab…don’t say you wouldn’t!