Download Secondary Physics: Food Lion Race Week

Secondary Physics:
Food Lion Race Week
Focus object or destination in the Hall:
Food Lion Race Week
Grade Level: Grades 9 – 12
Lesson Objectives: Students will
 Explain how springs, shocks and tension affect the ability of a car to stay on the track.
 Explain how impact force can be reduced with safety equipment during a wreck.
 Determine how machines give us mechanical advantage when completing a task.
 Describe how leverage is used to reduce input force when moving an object.
 Compare conceptually and mathematically situations involving potential-kinetic energy
transformations (pendulum, falling object, roller coaster, inclined plane, block-spring system)
indicating the amount of energy at various locations
 Define power as the rate of doing work (transferring energy), WPFvt==Δ
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.
Pre-Visit Activity
The following could be covered before your trip to the NASCAR Hall of Fame as an introduction or review of
Work, Power, Energy, Hooke’s Law, Machines, and Mechanical Advantage.
An Engine Dynamometer is a device for measuring force, moment of force (torque), or power. For example,
the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously
measuring torque and rotational speed (RPM). From a machine like this, an engine builder can determine
how much horsepower his engine has which correlates to speed in race cars.
Remember Power is how much work is done in a given amount of time. P= W/t
Students should be able to directly measure the stretch of a spring from equilibrium and the restoring force
corresponding to that amount of stretch by hanging various amounts of mass from a spring. Newton’s second
law states that the force of the Earth pulling down on the hanging mass is balanced by an upward force of the
spring on the hanging mass. Students should be familiar with finding the force of the Earth on a hanging mass
(its weight). A subsequent graph of spring force verses spring stretch should yield a linear relationship. The
slope of this graph represents the spring constant for that particular spring. The equation of this graph is
known as Hooke’s Law:
F = -k ∆x
The negative sign showing that the restoring force is in the opposite direction of the spring stretch.
Students can push on the two different springs. A comparison of their results should reveal different slopes
for each individual spring but a linear relationship for all springs.
Extension of Hooke’s Law
Teachers should show students that the area under the graph of spring force verses stretch represents the
energy stored in the spring.
Force
(N)
F
∆x
Stretch (m)
The area can be calculated by computing the area of the triangle of base ∆x and height F. This yield is:
Area = 1/2 ∆x F
Remember that F = k ∆x so through substitution one obtains:
Area = 1/2 ∆x (k ∆x) = 1/2 k ∆x2
This final relationship represents the elastic potential energy stored in the spring.
Q: Why does a car have springs?
A: Springs on race cars allow the cars to “drive” better. Most standard cars have the same springs in both
sides of the car. This is because they are turning left and right in equal amounts. NASCAR teams have to set
up their cars to turn left on the tracks. Therefore some springs on the left and right sides of the car have a
different stiffness. This stiffness allows the car to stay on the road better and absorb bumps in the pavement
without bouncing the car and causing the driver to lose control of the car.
Lesson 2: Food Lion Race Week
Engine and Power:
The Engine Dynamometer simulation demonstrates that this device measures force, moment of force
(torque), or power. For example, the power produced by an engine motor can be calculated by measuring
torque and rotational speed (RPM) at the same time. You can see that a NASCAR team of engineers puts every
engine through a test that compares its horsepower (hp) to revolutions per minute (rpm) for the engine. An
example of the results is reflected in the diagram below.
1. Directly behind you, at the V-8 Engine Evolution Mock exhibit, you will see that an engine can run
approximately 850 hp at about 900 rpm’s. If you convert this hp into Watts and use your equation for Power
(P=W/t), how much work does an engine do at this hp per minute?
1hp = 745.699872 watts
2. If this car travels one mile in 20s, what is the force the car’s engine is supplying?
Next find the “SUM OF ALL ITS PARTS” picture on the wall in the same room.
1. Can you tell where the springs on a car are located?
2. How many springs does a car have?
Once you have located the springs on the car make your way over to the two displays that show two large
springs enclosed with handles for you to push. Springs on cars allow the cars to “drive” better. Most standard
cars have the same springs in both sides of the car. This is because they are turning both left and right in
equal amounts. NASCAR teams have to set their cars up to turn left. Therefore some springs on the left and
right sides of the car have a different stiffness. This stiffness allows the car to stay on the road better and
absorb bumps in the pavement without bouncing the car and causing the driver to lose control.
1. What is the spring force on each of the springs you see? Use Hooke’s law to calculate your answer.
(F = -k
)
Make a simple graph of the springs to determine their stored potential energy. Use the graph below as a
model for your graph.
Area = 1/2 ∆x F
Force
(N)
F
∆x
Stretch
xx
Now make your way over to the Pit Crew Challenge and locate the jack and tire setup that compares a NASCAR
jack to a normal jack. In the Pit area at a NASCAR race, the crew must lift ½ the weight of the car to put on the
tires (the car weighs approximately 3400 lbs.).
1. If the car is lifted off the ground 5 inches how much work is done by the jack on the car?
2. A hydraulic jack is said to give a jack man a mechanical advantage of 40 when lifting a car. Knowing this, if a
car is lifted with a jack 5 inches and the handle is pushed down 20 inches, how much force is necessary to
push the jack down? MA= (Fr/Fe)
During a typical pit stop, the gas man must fill the tank of a car with 22 gallons of gas in less than 15 seconds.
This means that he must empty two 86 lb. gas cans into the car (each gas can hold 11 gallons of fuel). Try to
pick up the can.
3. How much force (Newton’s) is necessary to lift a gas can?
4. If the gas can itself weighs 12 lbs., how much does one gallon of gas weigh?
5. Each tire on a car weighs about 75 lbs. Pick one up for yourself. Does it feel about the same as the gas can?
Explain.
6. If a pit crew member must carry the tire a total of 9 feet to change it out during a pit stop, how much work
is he doing?