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FRICTIO FRICTIONAL FORCES

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**Free body diagram: A book lying on a level table**

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**Free body diagram: A person floating in still water**

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**Free body diagram: A wrecking ball hanging vertically from a cable**

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**Free body diagram: A helicopter hovering in place**

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**3 Free Body Diagrams: Move R, accel R Move R, no accel Move R, accel L**

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**Free Body Diagrams Notes**

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**Key Terms newton, - N, unit of force in the metric system**

- force needed to push a 1kg object at a speed of 1m/s for a second. mass, in physics, the quantity of matter in a body regardless of its volume or of any forces acting on it. weight, measure of the force of gravity on a body

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**What does gravity have to do with the weight of an object?**

Weight (W) varies depending upon the location of the body in the earth's gravitational field (or the gravitational field of some other astronomical body). The acceleration of gravity on earth is approximately: 9.8 m/s² in SI units and 32 ft/s² in US Customary units. To calculate the weight of an object you have to multiply it’s mass times the acceleration of gravity. W = m * g All objects fall at the same speed. Example: Feather vs. concrete block Air resistance is the only thing affecting how quickly the objects fall. Without that, they fall at the same speed.

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**The Statue of Liberty has a mass of 225,000 kg. How much does she weigh?**

To calculate the weight of an object you have to multiply it’s mass times the acceleration of gravity. Write the formula: W = m * g Substitute known values: W = (225,000 kg) * 9.8 m/s² Present solution with units: W = 2,200,000 N What the heck is 2,200,000 N? The Statue of Liberty weighs 2,207,250 Newtons, which is 495,000 lbs pounds!

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Free-Body Diagram A free-body diagram illustrates the relative magnitude and direction of all forces acting upon an object. The object must be isolated and “free” of its surroundings. lb This is a free-body diagram of the Statue of Liberty. She is represented by a simple box. The forces acting on her are labeled with a magnitude and the arrow shows direction. Notice the surrounding objects are stripped away and the forces acting on the object are shown.

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Free-Body Diagram “FW” here represents the force of the weight of the statue. “FN” is the normal force, which represents the force Liberty Island is pushing back up on the statue. FW = 495,000 lb Normal: means perpendicular to, (ex. The walls to the floor) The force of the pedestal to the statue is normal to the surface of the ground. FN = 495,000 lb The island has a great resistance to compression. The ground is exerting a force upward on the statue perpendicular, or normal, to the surface.

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**Free-Body Diagram Think of the diagram on an XY plane.**

If “up” is assumed to be the positive direction, then N is positive and W is negative. (Positive y-direction) +y FW = -495,000 lb When forces acting on the object cancel each other out it is in a state of static equilibrium. FN = 495,000 lb +x (Positive x-direction)

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**Force/Free Body Diagrams**

Create a free body diagram (FBD) of the gorilla: Gorilla FN FW Free Body Diagram of the Sitting Gorilla (The box represents the gorilla, W = weight of the gorilla, N = Normal force) Sitting Gorilla

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**Force/Free Body Diagrams**

Draw a FBD of the wooden swing: FT1 FT2 Where are the forces on the swing? Swing FW Free Body Diagram of the wooden swing (The box represents the wooden swing, W = weight of the swing and the parrot, T represents the ropes that are in tension supporting the weight) Parrot on wooden swing hung by ropes

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**Force/Free Body Diagrams**

Draw a FBD of bucket the bungee jumper leaped from: FT Where are the forces on the bucket? bucket FW Free Body Diagram of the bucket (T represents the tensile force of the cable the bucket is suspended from, and W is the weight of the diver and the bucket) Bungee jumping from crane

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**Force/Free Body Diagrams**

Draw a FBD of the ring at point C: Where are the forces on the ring? A B C D FTCA FTCB FTCD Free Body Diagram of the ring at point C (T represents the force of the cables that are in tension acting on the ring) Traffic Light supported by cables

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**Force/Free Body Diagrams**

Draw a FBD of the traffic light: FTCD Where are the forces on the light? A B C D Light FW Free Body Diagram of the traffic light (FTCD represents the force of the cables acting on the light and FW is the weight acting on the light) Traffic Light supported by cables

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**Force/Free Body Diagrams**

Draw a FBD of the pin at point A: Where are the forces on point A? A B E D C FTAB FTAC FTAE FTAD Free Body Diagram of pin A (If you consider the third dimension, then there is an additional force acting on point A into the paper: The force of the beam that connects the front of the bridge to the back of the bridge.) Pin-Connected Pratt Through Truss Bridge

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**Force/Free Body Diagrams**

Sitting Gorilla

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**Force/Free Body Diagrams**

Draw a FBD of the wooden swing: Where are the forces on the swing? Parrot on wooden swing hung by ropes

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**Force/Free Body Diagrams**

Draw a FBD of bucket the bungee jumper leaped from: Where are the forces on the bucket? Bungee jumping from crane

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**Force/Free Body Diagrams**

Draw a FBD of the ring at point C: Where are the forces on the ring? A B C D Traffic Light supported by cables

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**Force/Free Body Diagrams**

Draw a FBD of the traffic light: Where are the forces on the light? A B C D Traffic Light supported by cables

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**Force/Free Body Diagrams**

Draw a FBD of the pin at point A: Where are the forces on point A? A B E D C Pin-Connected Pratt Through Truss Bridge

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