Earth's Gravitational Pull

In addition to cannonizing his three laws of motion, Newton also created the Law of Universal Gravitation, which makes it possible to determine the force of gravity between two bodies, such as the Earth and the moon.

Lighter Than Air

Although the force of gravity applies to most everything on Earth, some objects, such as this balloon, are able to remain above the ground. This balloon can float because it is filled with helium, which is a gas lighter than those which comprise our atmosphere. This should not be taken to mean that the balloon is actually defying gravity. The balloon is still being pulled towards Earth, but because it is filled with a lighter gas than others in the atmosphere, a relatively stronger force is exerted on the heavier gases, allowing the balloon to float above them.

Analyzing Projectile Motion

"Flying Cat"

To better understand projectile motion, we can analyze its vertical and horizontal components separately. The main motion equations we can use to do this are V=V0 + at, X=X0 + V0t + 1/2at^2, and V^2=V^20 + 2a(X-X0). Each of these equations can be used in respect to either X or Y values. For example, the first equation can be used to find the Y component (vertical component) of a projectile motion: Vy= Vy0 + ayt. *Also, in such a case, ay would actually be the acceleration due to gravity, or -9.81 m/s^2.

Projectile Motion

The water being shot up by these fountains is an example of projectile motion.

Projectile motion is defined as the parabolic path taken by an object after it has been thrown. Because such an object is not self-propelled and air resistance can usually be neglected, the acceleration of the object is that of gravity and is assumed to be constant. Since gravity is pulling the object down during its motion, which is defined as being up, gravity is defined as being negative (-9.81 m/s^2). Given the object's initial velocity and the angle at which it was thrown, several different aspects of its motion can be calculated.

Deftying Gravity

If gravity pulls all objects within range towards Earth, how do some objects, like planes, defy gravity? So, the specific example of an airplane actually requires a long explanation for its ability to fly. This explanation involves the concept of the airplane's wings generating a lift by making use of Newton's laws, along with several other concepts. What is important to understand, however, is that because a plane has its own acceleration and power, in addition to an aerodynamic shape and other aspects, it is able to push against the force of gravity (which is still acting upon it), take off into the air, and remain airborne for an extended period of time.



Aerial view of California

"What goes up, must come down."

Gravity causes my dog to land on the ground seconds after he jumps, rather than continuing to gain height.

Gravity. What is it, exactly? Well, gravity is the name of the force that pulls objects towards the Earth's core- it's the reason that objects stay within Earth's atmosphere. This force has different magnitudes for different large objects. Since gravity is related to object mass, the pull of gravity on Earth is stronger than the one felt on the moon, for example. On Earth, the numerical constant for gravity is 9.81 m/s^2, or about 32 ft/s^2.