The Top Ten Equations of Physics

The following equations are among the most used in the world of physics:

10) Velocity = Distance / Time

This is a basic equation we learned early in the year.  It is used to find the rate of speed an object is traveling at.  Here is a sample problem:

A car goes 50 miles in 75 minutes, what is its overall velocity?
Answer- V = D/T so V = 50/75 = 2/3
*2/3 Meters per second

Velocity is measured in m/s because it is a rate of time.


9) Acceleration = Fnet / Mass

This is not just an equation, it is Newton's Second Law of Motion, which specifically states that Acceleration is inversely proportional to mass, and directly proportional to Fnet.


8) Universal Gravitational Law- F = G m1 X m2 / d^2

The Universal Gravitational Law is very important to physics because it allows us to find the gravitational attraction between two large objects, planets, for example.  Another important factor that comes from this law is that as distance increases, the force between the two objects decreases.  Likewise, as the distance decreases, the force will increase.  This is why, if astronauts want to fly by other planets, they must not get too close, or the gravitational force of attraction will increase and they will be pulled into the planet.



7) Torque = Lever Arm X Force

This is a very important equation because it helps us to understand why, for instance, a longer wrench will work better in turning a bolt.  Since torque is jointly proportional to lever arm and the force, if you increase either one of the two, you will increase the torque.  So, if a bolt is incredibly hard to screw, you don't need to be extremely tough, you just need a bigger wrench.


6) Momentum = Mass X Velocity, P = mv

As shown by the equation, momentum is the product of the mass and velocity of an object.  The most interesting thing about this equation is that it shows that an object can have very little mass, but still have alot of momentum, like the remote-controlled car in this video:

5) Work = Force X Distance

Work is the product of force and distance an object is pushed.  Work can only occur if the force and the distance moved are parallel.  For example, if I were to carry a book across a room, my force on the book and the distance would be parallel, and no work would occur.  Here is an example problem:

If a 100 N man runs up a 7 meter high stair case, he produces 700 Joules of work.  It does not matter how fast he moves, because that is not part of the equation.


4) How Far (Free Fall)   D = 1/2 g t^2

This equation is important because it shows us how to know how far an object has fallen when no other forces are acting on it (air resistance, wind).


3) Kinetic Energy = 1/2 m v^2

Kinetic energy is the energy of moving things.  This equation allows us to determine the Kinetic Energy in a moving object at any given moment.  Kinetic Energy is also proportional to work because of the equation, (delta)KE = Work.  Here is an example:

A ball has a mass of 20 g, and it is moving at 100 m/s.  What is its Kinetic Energy?
- KE = 1/2 (20) (100^2) = 10 (10000) = 100000


2) Potential Energy = mass X gravity X height

Potential Energy is the opposite of Kinetic energy in that, it is found in stationary objects.  Also, height is a very important factor.  The higher you raise an object, the more potential energy it will have.  Here is an example:

A 10 g rock is on the edge of a cliff 50 m up.  How much PE does it have?
- PE = mgh = 10(10)(50) = 100(50)= 5000


1) OHM'S LAW- Current = Voltage/ Resistance

This is the most important equation in all of physics.  It shows us that as you increase the resistance, the current will decrease because the two are inversely proportional.  Electricity is a huge part of our every day lives.  So, it is imperative that we have a solid understanding of current and how it works in our homes.  If we do not use fuses, which cause the circuit to break if there is too much current, houses could catch on fire from all the current.

The Physics of a LAX Goalie

The Physics of a LAX Goalie

Jules R. Gonsoulin

You wouldn't guess it at first, but the goalie actually controls the speed and flow of a lacrosse game.  He is the "defensive quarterback".  He needs to know how to make good outlet passes.  Outlet passes are made after a save and are used to send the ball back down the field.  In order for an outlet pass to be successful, it needs to have height and speed.  That is where PHYSICS come into play.

The most important concept to understand is that the height of a projectile controls the amount of time it is in the air.  This is due to the equation, d = 1/2 g t^2.  The longer an object is in the air, the farther it will go.  Thus, you want to release the ball when it is at its highest point, so it will stay in the air for a long time, and you can complete long, full-field passes.

Tangential speed also comes into play here.  The farther away an object is from its center of rotation, the faster it will have to move to keep up with the center.  Since the stick is a rotating body, the objects farthest from the center of rotation will have the most horizontal velocity when released.  Since the ball is the farthest object from the center, it will move very quickly out of the stick.  If you can get the ball to move faster, your passes will be completed quicker, and your clears will be more efficient.

Principles Represented:

• Torque
• Rotational Motion
• Tangential Speed
• Projectile Motion

IDENTIFICATION- This photo is natural.

Unit 8 Reflection

In unit 8 of Physics, we studied magnetism and how it relates to electricity.  The concepts in this chapter were a  little hard to grasp, so I had to study alot outside of regular homework assignments.

The first topic we discussed was magnetic poles.  Every magnet has north and south poles.  Opposite poles attract, and same poles repel.  If a magnet were to be broken into two, there would be two equally strong magnets with their own poles.

Magnetism is produced by the motion of spinning charges called domains.  If the domains are all spinning in the same direction, or flowing in the same direction, they create a magnetic field.  Here is an image showing everything discussed so far:

As you can see, the flow of charges is from the south pole to the north pole.  The blue circle in the middle could in fact be Earth.  Earth is a magnet!  We have a North pole and a South pole.  More importantly, Earth's magnetic field protects us from harmful cosmic rays at most areas of the planet.  The rays cannot penetrate the magnetic field at the sides because they are going perpendicular to the magnetic field.  However, the rays can enter through the north or south pole, because they are moving parallel to the magnetic field.  This causes the popular "Northern Lights".

Another thing we talked about were motors.  Motors are simple apparatuses.  They are made up of an energy source, a magnet, and an armature of current carrying copper wire.  The energy source supplies energy to flow through the system, while the magnet creates a magnetic field.  When you turn it on, the armature feels a torque from the magnet and turns constantly in one way.  We made motors like this in class using a batter as our energy source.  The most important part was shaving the wire.  We could only shave on the bottom of the wire or else it would be pulled in different directions, and not flow steadily.  Here is a video of my motor at work:

Our next order of business was Electromagnetic Induction.  This was a tricky concept to understand.  The long and short of it is, when a magnet passes by a loop of wire, it induces a voltage, changing the current.  This is one of the most important aspects of physics, and it has been used to build appliances and machines all over the world throughout time.

In class, we looked very carefully at generators.  Generators use rotating coils and stationary magnets to turn mechanical energy into electric current.  A generator is essentially the opposite of a motor, in that a motor turns electric energy into mechanical energy and a generator turns mechanical energy into electrical energy.  This makes generators perfect for situations when there is a power surge.

Possibly the most important item we talked about was the Transformer.  A transformer has the ability to either step down or step up the value of voltage flowing through it.  It is made up of two coils of wire, one with more turns than the other.  When one magnetic field changes, it changes the other magnetic field, inducing a voltage.  It looks like this:

The purpose of a transformer is usually to keep objects plugged into the wall from burning up from the 120 Volts that come out.  Have you ever seen this little box on your laptop charger?

Yes, that is a transformer.  Since your computer can only handle about 10 volts, you need to step down the energy.  That is what this little box does.  This box gets very hot when it is in use because of the great value of voltage flowing through it.  It is important to note that transformers must use Alternating Current, so that the particles can change directions, in turn change the magnetic field about the primary.  If you must use DC, you have to turn the object on and off repeatedly to make the transformer work.

Overall, this chapter required a lot of memorization of basic concepts.  However, after I did memorize that stuff, it wasn't hard to synthesize it all into real world problems.  I really liked building the motor.  It helped me really visualize what we were talking about.