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Forces and Motion

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Kieran Hawson

on 6 March 2013

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Transcript of Forces and Motion

By Cameron Hawson Motion and Forces Motion is one of the most important parts of physics. Everything in the universe moves. Now, it might be very, very slow, but it is still moving. Remember that even if you're lying on your bed, the Earth is still rotating around the Sun and the Sun is still moving around the galaxy. Movement is constant.

Over the years, scientists have also discovered laws that explain motion and what causes changes in motion.

What is Motion? When we want to measure motion, it's important to know how fast the motion is. Two terms you need to know are speed and velocity. They are different!

Speed describes how fast an object is moving,

Velocity is the rate of motion in a specific direction. It is a vector. So you could describe the speed of a car driving from Albuquerque to Santa Fe as 75 mph, but the velocity of that same car would be 75 mph north.
How is Motion Measured? Newton's Laws of Motion talk a lot about forces. That's because forces are a big part of physics. Forces can be found everywhere in the universe. They can be very large, like the pull on a planet by a star, or very small, like the pull of a nucleus of an atom on an electron. Very simply put, a force is a push or a pull.

Force is measured, conveniently enough, in Newtons (N). Wonder where they came up with that?

There are four fundamental forces of nature: Gravity, Electromagnetism, the Strong force, and the Weak force. These forces act upon the universe all the time. Forces of Nature Gravity is a force of attraction. I don't mean finding someone really cute. I mean the Earth pulling on you and keeping you on the ground. That's gravity.

Every object in the universe that has mass exerts a gravitational pull on every other object. You exert gravity on things around you, but since you're not very big, your pull isn't really noticeable. However, when you're talking about really large masses like the Earth or the Moon, then you're talking about some serious gravity!

The Earth has enough gravitational pull to keep the gases in our atmosphere here instead of floating away in space. Gravity Electromagnetism is the interaction of particles with an electrical charge. We know it from using a magnet where the magnet is attracted to particles in metal objects which pulls the things towards it. This force can push other magnetic objects away by turning the magnet around and changing the direction (polarity) of the magnetic field.

Scientists used to think that electricity and magnetism were two different forces, but a physicist named James Clerk Maxwell proved they were unified using Maxwell's equations. Electromagnetism The strong force is what holds the nucleus of an atom together. It doesn't have a very long range, but it is very important, because it is literally what holds things in the universe together, like glue. Strong Force The weak force is sort of the opposite of the strong force. While the strong force holds things together, the weak force breaks them down. It is responsible for the radioactive decay of atoms. Weak Force Simple Machines are objects that can be used to make certain tasks easier. They can be used to make very big jobs go faster and require less energy to do. They can help out with many things that you would do every day. They maximize force output with the minimum of force input. What a deal! Simple Machines A lever is an example of a simple machine. It is made from a straight piece of wood or metal that you can then use to pry open things, or lift up heavy objects. In addition, if you put it on a fulcrum, which is anything the lever balances on, and then place an object on one side and push down on the other, you can propel the object. Lever An Inclined Plane is a ramp. It makes it easier to move things up by pushing them up a ramp which reduces the amount of strength required to move the object. It also will help you accelerate if you go down the ramp because of the downward angle. Inclined Plane A pulley is a wheel on an axel that is designed to hold a rope or cable. You can also attach something to an end of the rope and pull it towards you. This is an effective tool to pull and transport different things to different places. It does not require a lot of strength to move objects because if you balance the weight on both sides, it doesn't feel very heavy. Pulley A Wheel/Axel is when a wheel is on a pole (this is called an axel) and they are used together to move certain objects. On a cart there are wheels which are connected to axels which makes the cart move forwards. This simple machine can be seen on cars, motorcycles, bicycles, tricycles, scooters, and many other things that move with wheels. Wheel/Axel


THANK YOU!!! Screw A screw is a mechanism that converts rotational motion(turning something around and around) to linear motion (forwards or backwards).The most common form consists of a shaft with grooves or ridges called threads around the outside.The screw passes through a hole in another object, with threads on the inside of the hole that mesh with the screw's threads.When the shaft of the screw is rotated through the stationary threads, the screw moves forward. A good example is screwing a wood screw into a piece of wood. Wedge A wedge is a triangular shaped tool, made out of a compound and portable inclined plane. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by converting a force applied to its blunt end into forces perpendicular to its inclined surfaces. The mechanical advantage of a wedge is given by the ratio of the length of its slope to its width. c http://www.robives.com/mechs levers and pulleys http://www.mikids.com/Smachines.htm Math lesson: Calculating Acceleration Acceleration is defined as the rate at which the velocity of an object changes. In other words, acceleration is a measure of how quickly something speeds up or slows down. The equation for acceleration is given below:

EQUATION:
change in velocity = final velocity - initial velocity

acceleration = change in velocity
---------------------
time

Motion doesn't just happen on its own. It is caused by forces. Forces act upon an object to get it moving or change its motion. What causes motion? Acceleration Acceleration is when velocity is changing. It is a vector, too. When velocity and acceleration are both going in the same direction, you speed up. But if they're going in opposite directions, you slow down or decelerate. Acceleration is a measure of how much the velocity of an object changes over a certain period of time (usually in one second.) Calculating Acceleration PROBLEM:
Calculate the acceleration of the ball for each
time period that it falls.
a.
b.
c. Calculating Acceleration PROBLEM:
What is the acceleration of an in-line skater who increases her velocity from 3.5 m/s forward to
6 m/s forward in 2 seconds?


Answer: change in velocity = 6 m/s - 3.5 m/s = 2.5 m/s

acceleration = 2.5 m/s
------------
2 sec.

acceleration = 1.25 m/s squared forward Answers: a. 4.9 m/s - 0 m/s = 4.9 m/s
4.9 m/s
--------------
0.5 sec = 9.8 m/s squared downward

b. 12,25 m/s - 4.9 m/s = 7.35 m/s
7.35 m/s
-----------------
0.75 sec = 9.8 m/s squared downward

c. 31.85 m/s - 12/25 m/s = 19.6 m/s
19.6 m/s
------------------
2 sec = 9.8 m/s squared downward
Newton's Laws of Motion Sir Isaac Newton was from England and he spent a lot a time experimenting with motion (and apples.) He worked on calculus and physics and was the first person to come up with three basic ideas about motion.

Since then, we've tested them, and tested them, and tested them some more and they still work, so we now call them Newton's Three Laws of Motion. Newton's 1st Law of Motion The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same direction and speed. Newton's 2nd Law of Motion The Second Law is also known as the following equation: F = ma
Force is equal to the mass of an object multiplied by the acceleration. What this means is the more force you apply to something, the greater the acceleration will be. Also, the second law shows that if you exert the same amount of force on two objects that have different masses, you will get two different accelerations. The acceleration of the smaller object will be greater than of the bigger object.

So the effect of, say, a 20 Newton force on a baseball is going to be a lot more than on a huge truck because of the difference in mass. Newton's 3rd Law of Motion The Third Law says that for every action there is an equal and opposite reaction. Forces come in pairs. So when you sit in a chair, you are exerting force down on the chair, and the chair is exerting force upward to keep you from falling on your butt.

Another example is firing a cannon. When the cannonball is fired, the cannon moves backward. The forward motion of the cannonball is balanced by the backwards movement of the cannon, but you notice the backwards movement less because the cannon has a much bigger mass than the cannonball. Friction Although friction is not a fundamental force of nature, it is very important, so I'm going to talk about it here.

Friction is a force that holds back the movement of a sliding object.

Anytime objects come into contact with each other, there is going to be friction. Friction acts in the opposite direction of where the object is sliding so it slows the object down.

Friction technically only works on solids, but you can see the effects of more or less friction on liquids and gases. For example, cars skid on a wet road because the water reduces friction. And the space shuttle heats up when reentering the atmosphere because of the friction caused by air resistance.
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