In order to understand why the North American Eagle® car behaves the way it does when being driven, you need to understand some basic concepts about physics. Physics has to do with the laws of Science about energy, forces, and motion.
Energy is defined as the capacity for doing work and overcoming resistance. For the NAE™ car, energy is produced from burning fossil fuel, or kerosene, in the jet engine inside the car. Of course, the resistance the car must overcome with the energy generated by the engine are a combination of three things; the mass of the car (7.5 tons), the gravitational forces of our planet acting upon that mass, as well as the friction and drag acting upon the car’s shape.
Force is defined as any “push” or “pull” on an object which causes that object to move. (See motion below.) The “work” the jet engine does is called thrust. This thrust is force which pushes against the car’s mass and overcomes the resistance, or inertia, due to the car’s mass.
You probably understand mass in terms of weight, but weight is only a measure of the force from gravity pulling down on things; which is another force acting on all of us on Earth. Scientists however, refer to mass because it is an indication of how much matter is concentrated in some object. Inertia will be explained in more detail later on, but to understand it you can think of something you’re probably familiar with.
If you’ve ever ridden a bicycle, you know how hard it is to start pedaling when you first start out. However, as you gain speed on a level area, it becomes easier to keep pedaling. The reason why it’s harder to start pedaling is because your leg muscles are working against the mass, or weight, of both your body and the bike to get moving. Now, if you stop pedaling the bike, but just let the wheels roll on the level surface, it keeps going along rather well for a good distance. This is because your and the bike’s mass are now in motion. You would stay in motion if no opposing force acted against your mass. When you push down on the pedals backwards to make the brakes work, or you squeeze the brake handles, an opposing force is used. This is making an opposing force, called friction, acting against the inertial motion of the bike to slow it down to a stop. Inertia is one of the laws of physics discovered by Sir Issac Newton who said, “An object at rest will remain at rest unless acted on by a force, and an object in motion will remain in motion unless acted on by an opposing force.” This law is known as the 2nd Law of Physics.
So, the car’s engine pushes it along faster and faster. Because the engine can generate so much force, or thrust, it can keep the speed of the car increasing as the very heavy mass of the car is gradually overcome. Now the car is in motion and gaining speed. This is known as acceleration.
Motion is defined as the ability to measure an object’s movement from one point in space to another over a unit of time. When it comes to the NAE™ car, we are talking about it rolling along the flat dry mud lake bed surface. Over distance (nearly 4 miles) and time (around 90 seconds), the car continues to gain speed; 100, 200, 300, 400, 500, 600 MPH and up. At this speed, the car travels over one mile in a time of only about six seconds. This continual increase in speed over distance is called acceleration. At 630 MPH the car is approaching what is called the “transonic zone”. This means that because the car is pushing through air so fast, the particles of air are beginning to affect the car and flow over it like a fluid, or like when you are moving through water in a pool.
One of the more interesting results of the car traveling at transonic and supersonic speeds is the affect of the build up of the shock wave as it moves along so close to the ground. This phenomenon can be seen in the pictures of the ThrustSSC during record runs over ten years ago. This same affect is produced by jet aircraft traveling at very low altitude over water; as the pictures below reveal.
The result of this shock, the ThrustSSC team found, was that the playa where the car was traveling at transonic and supersonic speeds was as though someone had drug a huge rake along that section; it was all churned up.
Doppler Effect on Sound
Have you ever noticed how an object, say a plane flying toward you makes a higher pitched noise than when it passes and makes a lower pitched sound? This same affect is what the team will experience as the NAE™ travels supersonic across the lake bed when setting the record.
Remember to visit the page on Mathematics of LSR to read more information on the physics which play into how this vehicle will behave.
More to come soon. Especially now that we will soon have CFD analysis on the car.