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Things You Need to Know
- A "free-body diagram" is an illustration showing all the forces acting on a given object.
- The vector sum of all the forces acting on a given object is called the net force.
- If the net force is not zero, this means there will be an acceleration of that object in the direction of that net force.
- Newton's First Law:
- “An object will continue either being at rest or moving at constant velocity unless acted upon by an external non-zero net force.”
- Newton's Second Law:
- “When an external non-zero net force acts on an object, the object accelerates in the direction of the net force. The magnitude of the acceleration is directly proportional to the magnitude of the net force, and inversely proportional to the mass of the object.”
- Or, more simply: Fnet = ma
- Newton's Third Law:
- "For every action, there is a reaction that is equal in magnitude, but opposite in direction."
- This law describes action-reaction contact forces between two objects.
- "Weight" refers to your force of gravity, in Newtons.
- Your weight depends on which planet you're on, or whether you're accelerating up/down.
- "Mass" is a measurement of the matter in an object, measured in kilograms.
- It's the same everywhere in the universe.
- In elevator questions, there is tension force FT going up, and gravitational force Fg going down. Your Fnet is equal to the larger force minus the smaller force, and indicates which direction the elevator will accelerate.
- FT is also a representation of your "apparent weight".
- The "coefficient of friction", μ, determines how strong the force of friction is between two surfaces.
- A lower value for μ indicates a more "slippery" surface.
- Ff = μ(FN)
- On an inclined plane, you have several forces to keep track of (see side picture).
- Ultimately, it almost all comes down to the true Fg.
- Fg is the hypotenuse of a right triangle formed with either Fg(perp) or Fg(parallel).
- Newton's Law of Universal Gravitation tells you the force of gravity between any two objects: Fg = (Gm1m2)/r²
- Note that G = 6.67 x 10^(-11)
- Also note that "r" is the distance between the CENTER of each object.
- The rate of gravitational acceleration, also called the gravitational field strength, is denoted by lowercase g.
- g = Gm/r²
- m is the mass of the object creating the gravitational field (usually a planet/moon/star).
- g = Gm/r²
Homework Assignment
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Newton's Laws Homework | |
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