Secondary Physics: The Compass Rose, Cars and Tracks

Transcription

1 Secondary Physics: The Compass Rose, Cars and Tracks Secondary Physics at the NASCAR Hall of Fame The Great Hall and Glory Road Focus object or destination in the Hall: Compass Rose, 18 compass lines, and the cars and tracks on Glory Road Grade Level: Grades 9 12 Lesson Objectives: Students will Explain why there are various degrees of banking found in NASCAR and the impact of speed and various force. Describe how friction force affects a cars ability to maintain its speed on the track. Define vector and scalar, incorporating magnitude and direction. Apply concepts of speed and velocity to solve conceptual and quantitative problems. Distinguish between distance and displacement conceptually and mathematically. Clarify that a positive value for velocity indicates motion in one direction while a negative value indicates motion in the opposite direction. North Carolina Standard Course of Study Objectives for High School Physics: Phy.1.1 Analyze the motion of objects. Phy.1.2 Analyze systems of forces and their interaction with matter. Phy.1.3 Analyze the motion of objects based on the principles of conservation of momentum, conservation of energy and impulse. Phy.2.1 Understand the concepts of work, energy, and power, as well as the relationship among them. Vocabulary: Degrees of banking, vector quantities, velocity, speed springs, shocks, free body diagrams, friction, normal force, torque, leverage, mechanical advantage, momentum, impact.

2 Pre-Visit Activity The following could be covered before your trip to the Hall either as an introduction or review of Motion and Force. Q: If there was little to no friction between a car's tires and the road it traveled on, could the car still get around a curve or would it keep traveling in a straight line? A: Well, yes, it could happen if the curve was banked, and the car was traveling the correct speed. Q: Can you explain this? A: Answers may vary but all should include some of the following conceptual thoughts. If a car is on a level (unbanked) surface, the forces acting on the car are only its weight, mg, pulling the car downward, and the normal force, N, road on the car, which pushes the car upward. Both of these forces act in the y direction and have no x component. If there is no friction, there is no force that can supply the centripetal force required to make the car move in a circular path therefore there is no way that the car can turn. On the other hand, if the car is on a banked turn, the normal force (which is always perpendicular to the road's surface) is no longer vertical. The normal force now has a horizontal component, and this component will now act as the centripetal force on the car! If the car travels with the right speed so that its centripetal force equals this available force, a car can safely negotiate a banked curve! Sample Problem 1: A turn with a radius of 100 m is being designed for a maximum speed of 25 m/s. What angle should the turn be banked in order for the car to be able to go around it without any friction force between the tires and road? Solution: radius of turn, r = 100 m speed of car, v = 25 m/s free-fall acceleration, g = 9.8 m/s 2 bank angle, =? From the free-body diagram for the car:

3 So, the banking angle should be about 33 o, just like our super speedways! Sample Problem 2: Talladega Motor Speedway has turns with radius 1,100 ft. that are banked at 33 o. What is the "no friction force" speed for a car here? Solution: We can use a free-body diagram and get from that: Thought Question: So, a car going 100 mph could negotiate the turns at Talladega without any friction force. During a NASCAR race, however, the cars go through the turns at nearly 200 mph... How?

4 The Great Hall and The Compass Rose Charlotte, North Carolina is the location of the NASCAR Hall of Fame and it has a compass rose located in the Great Hall that designates Charlotte as the home of NASCAR. The compass rose also has 18 compass lines that denote a racetrack, its location, and the mileage from Charlotte as the crow flies (the shortest route between two points). 1. Can you explain why it will probably take longer to drive to one of these tracks than it takes the crow to get there? 2. The exhibit you are looking at shows the distances with an arrow pointing a specific direction to make these vector quantities. How could we express one of these distances quantitatively (without the arrows) but still express to someone the same information? 3a. If you are traveling at 65 mph, how long would it take to arrive at the Charlotte Motor Speedway as the crow flies? Projectile Motion: 3b. Neglecting air resistance, if someone fired a projectile at 45 o that landed at the speedway in the same amount of time, how fast would it be traveling in the X and Y directions upon impact? 3c. What is the maximum height this object would have to reach to achieve its target?

5 Walking Around Glory Road If there was little to no friction between a car's tires and the road it traveled on, could the car still get around a curve or would it keep traveling in a straight line? Well, yes, it could happen if the curve was banked, and the car was traveling the correct speed. 1. Pick a car on Glory Road that is on the flat part of the track and draw a free body diagram for the forces acting on the car. Identify your car with a label (driver, car model, and a year). 2. Find the NASCAR Truck on Glory Road and draw a free body diagram of it just as you see it. Be sure to include the correct degree of banking. 3. Who drove this truck and what track uses this banking? 4. Calculate the Fnormal for this vehicle assuming it has a weight of approximate weight of 3400 lbs. Hint: you must first convert pounds to Newtons! (1.000lb = Newtons)