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Chapter 4: Lesson 1 - Forces
Chapter 4: Lesson 1 - Forces
A force is a push or a pull on an object. We abbreviate force with a capital F. There are two basic types of forces, action at a distance and contact.
Action at a distance forces happen when contact between two objects are not necessary, they can be some distance away from each other.
Contact forces happen when two objects are touching.
The SI unit for force is a NEWTON! A Newton is slightly less than a quarter pound. I always give the analogy that a newton is just like a cooked quarter pounder without the bun, cheese, and condiments. The patty starts off as a quarter pound of meat, but by the time it is cooked, and some of the fat and juices are gone, it is slightly less than a quarter pound... roughly one Newton.
The next time you want to order a quarter pounder with cheese at McDonalds, you could order a Newton with cheese.
A Newton is abbreviated with a capital N because it is named after a person... Sir Isaac Newton!
Examples of Action at a Distance Forces:
Examples of Action at a Distance Forces:
These are forces that you have probably studied in Chemistry. Other than gravitational force, we will not concentrate on the other action at a distance forces in CP Phyiscs.
Gravitational Force: This force is both an action at a distance and a contact force. If you drop something, gravity accelerates that object toward the earth. Gravitational force can happen when you are touching something or at a distance from something.
Electromagnetic Force: This force give materials their strength, and ability to bend, stretch, squeeze, or shatter.
Strong Nuclear Force: This forces holds particles in the nucleus together.
Weak Nuclear Force: This force is involved in the radioactive decay of some nuclei.
Examples of Contact Forces:
Examples of Contact Forces:
These are EXTREMELY important to know! We will be using these forces a lot throughout the entire year.
Applied Force: Abbreviated Fapp this force is the force that we APPLY to an object. If you are pushing a box down the hallway, you are applying a force to the box, aka, the applied force.
Gravitational Force or Weight: Abbreviated Fg or Fw this force is gravity pulling on your mass. It is what you feel on your feet when you stand up, or on your bum when you are sitting down.
Normal Force: Abbreviated Fnorm this force is a support force. When we stand normally, we are perpendicular to the floor. The normal force is the perpendicular force that supports us. We are pushing down on the floor with our weight and the floor is pushing back up at us with the normal force.
Frictional Force: Abbreviated Ff this force is an opposing force. It opposes motion. Friction is what helps us walk. The less friction there is on the ground, the harder it is to walk. Friction is always pointing in the opposite direction to the applied force.
Air Resistance: Abbreviated Fair this force is also an opposing force. It points in the opposite direction of motion when objects are moving through the air.
Tensional Force: Abbreviated Ftens this force is found in ropes or strings. There is a lot of tension on that tug-o-war rope during each pep rally!
Spring Force: Abbreviated Fsp this force is found in springs.
Check Your Understanding:
Check Your Understanding:
For the four questions below, think about the question, then click on the down arrow when you have your answer to check to see if you are correct.
What force supports your body weight as you sit on a chair?
Normal Force - it is ALWAYS perpendicular to the surface that you are sitting on!
2. What force is present when two surfaces are touching? It always points in the opposite direction of the applied force.
Friction
3. When you are standing on the floor, this is the force that is pushing down on the floor.
Gravitational Force or Weight. Do not say gravity! Gravity is an acceleration and not a force! Gravity pushing on our mass is the force, which is the gravitational force.
4. When you push your desk next to your friend's desk in class, this is what we call the force of you pushing your desk.
Applied force
Fun Video on Friction!
Fun Video on Friction!
The mythbusters take on many physics concepts and in this short clip, they were looking at friction. They interleaved the pages of two phone books together and then tried to pull them apart. Watch the video to see what it took to separate the two phone books!
You have finished Lesson 1!
You have finished Lesson 1!
Be sure to head over to google classroom and fill out the exit pass.
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