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Roller Coaster Dynamics 2 Lab Summary
Friction, Losses, and Centripetal Force
Losses play an important role in the roller coaster project. The primary losses considered in the project are losses
due to friction. Understanding Normal force is important to understand the concept of friction. Try to understand
the normal forces the ball encounters on different sections of the track (loops, ramps, flat sections) and the
frictional forces that result.
Concepts/Definitions:
w  mg
Weight:
The force due to gravity.
Normal Force:
Friction:
A force resulting from two objects ‘pressing’ against each other.
This force acts perpendicular to the area of contact (see example below).
In the context of the project the normal force often results from the weight
force of the ball. A special case to consider is the normal forces the ball
experiences when going through a curved section of the track such as a horizontal
or vertical loop.
A force that opposes motion/action. Two forms: static and kinetic.
Static Fsf   s N
where  s is the coefficient of static friction and N is the
normal force. This is the force encountered when trying
to move a stationary object. The ball isn’t stationary in the
roller coaster project, it’s rolling along the track, so why
care about static friction? Static friction is the force that
makes the ball roll along the track instead of sliding along.
Kinetic Fkf   k N
Centripetal Force:
V
Fc
Fc 
mv 2
R
where  k is the coefficient of kinetic friction and N is the
normal force. This is the friction encountered by a moving
object.
where m is the mass of the ball, v is the velocity of the ball,
and R is the radius of the curve. This is a force the ball
experiences when traveling on a curved path such as a turn
or a horizontal or vertical loop. This force points towards
the center of the curve at all points along the curve (see
figure at left from lab slides, rotate it mentally). The
centripetal force will cause losses since the ball is pressing
against the track resulting in friction.
Example: Static Friction
Assume object mass m resting on a flat surface,
gravity g, and coefficient of static friction  s
What is the weight of the ball?
W  mg
What is the normal force on the ball from the surface?
N  W since the surface is ‘flat’
What is the static frictional force right before the object
moves on the surface?
Fs   s N   sW   s mg