Roller Coaster Design Project Lab 3: Coaster Physics Part 2

Transcription

1 Roller Coaster Design Project Lab 3: Coaster Physics Part 2

2 Introduction The focus of today's lab is on the understanding how various features influence the movement and energy loss of the ball. Loops - Understanding centripetal acceleration and how to calculate the frictional losses in a loop Hills - Understanding the effects of momentum and projectile motion and how to ensure the ball remains on the track Banks - Modeling G-forces in banked turns and estimating energy loss

3 Forces Involved in the Coaster

4 Centripetal Force To move along a curved path requires centripetal force This force is pointed inward toward the center point of the circle (or arc) along which the object moves The ball applies an equal and opposite force to the track, called the reactive centrifugal force Centripetal force (and thus centrifugal force) for a given velocity, v and radius R, can be found with the equation:

5 Gravitational Force At all times, gravity acts upon the ball This force is pointed directly downward at all times Can be found using the following equation: F g = ma = mg

6 Normal Forces Normal forces are the result of two objects pressing against one another. Normal forces are always perpendicular to the plane surfaces that are pressing together Frictional losses in the coaster will scale with the normal forces

7 Free Body Diagrams

8 Free Body Diagrams (FBDs) Simple illustration of the scenario to be analysed showing all forces on the body and where they are acting For the coaster, we will include gravitational, centripetal, centrifugal and normal forces We will use vector mathematics & trigonometry to find the relevant components of each force Goal: calculate the total force normal to the track at a given point.

9 FBD Example 1

10 FBD Example 2 The green vector contributes to the normal force. How do we find it? W*cos(Θ)

11 FBD Example 3 - Loop In this case, the ball is traveling through the loop. There are 3 key scenarios: The bottom of the loop The side of the loop The top of the loop How do we the normal force at each point?

12 FBD Example 3 - Loop Bottom Bottom of the loop As the track curves up, the ball is pressed into the track in the same direction as gravitational force Gravitational force (green arrow) and reactive centrifugal force (blue arrow) are modeled as additive when finding the normal force Frictional loss scales with total force perpendicular to the track Gravitational Force Motion Reactive Centrifugal Force

13 FBD Example 3 - Loop Sides Sides of the loop Gravity and centrifugal force are perpendicular. We can model the normal force as being equal to F C only

14 FBD Example 3 - Loop Top Top of the loop Gravity and centrifugal force oppose one another. In this case, the normal force is modeled as (F C - W) Additionally, to keep the ball on the track, the balls velocity must be great enough for the centrifugal force to overcome gravity.

15 FBD Example 3 - Loop Consider: The (very rough) average force felt by the track from the ball is: or: So the average force felt by the track from the ball through the loop is equal to F C! Note: This is a VERY rough approximation!

16 FBD Example 4 - Bank Model When the ball travels around a banked turn, centripetal forces again play a roll. In this example, we will look at a cross section of track Note that both weight and centrifugal force contribute to the counter force to the normal force Use the bank angle and trig to find these components and add them Turn Center Normal Force

17 FBD Example 5 - Hill We can model a hill or bump on the coaster as the exterior of a circular loop. As with the loop top, gravity and centrifugal force oppose one another. Now, to keep the ball on the track, the balls velocity must be small enough for the centrifugal force to NOT overcome gravity.

18 Questions?