Law of Acceleration

Remember that Newton's first law stated that an object with no net force acting on it will not accelerate. Newton's second law of motion, though, states that an unbalanced force (one that is not equally opposed by another force) acting on an object will cause the object to accelerate. The object's mass, which measures its inertia, also determines how much the object's movement will change. From this, Newton derived the formula a= F/m, where acceleration is directly proportional to force and inversely proportional to object mass. 

The Law of Inertia

Newton's first law states that an object has a certain inertia, which allows it to resist a change in its state. Mass is the measure of this inertia, and is measured in kilograms (if using SI units). As a result of this inertia, an object that is at rest will remain at rest, and one with a constant velocity will continue moving with that velocity, unless acted upon by another object.


Unless something moves this turtle, it will remain still until it chooses to move.

How Sharp is Too Sharp?

Although we may not think about it, the roads on which we drive are an application of physics. When they have to calculate the maximum degree until which a curve is safe for a car to make, engineers need to consider friction. Friction is defined as the resistance that one surface or object encounters when moving over another. It is what allows people to walk forward and cars to drive onward; without it, we would all remain in the same place, regardless of how much we tried to move. Engineers also use this concept when deciding on a safe maximum speed at which cars should drive (speed limit).

Energy Transfer

So I didn't have a picture of this one. Instead, I got it from http://eisforexplore.blogspot.com/2012/03/energy-transfer-for-kids.html, although I searched for it after planning my post.

When you drop a tennis ball placed on top of a basketball, the tennis ball bounces higher than it does when dropped alone, and the basketball does not bounce as high. When trying to understand this, take into account the energy transfer that takes place when the two balls come into contact. As the basketball begins to rebound, it hits the downward-falling tennis ball, thereby transfering some of its (the basketball's) energy to it (the tennis ball). For this reason, the basketball has less energy and therefore attains a lower height, while the tennis ball gains altitude.

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.