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Chapter 11.3 Pages 380 - 385

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Any action that can change the state of motion of an object

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1. Force of gravity – example: Earth’s pull on all objects on it. 2. Electromagnetic force – example: force produced by electricity 3. Strong nuclear force – force that keeps protons in the nucleus together 4. Weak nuclear force – observed during radioactive decay

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Total Force on an object

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If forces act in the same direction on an object, you need to add the forces. If forces act in opposite directions on an object, you need to subtract the forces.

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Forces are balanced if the net force is equal to zero. The object must be at rest or moving at a constant velocity.

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Forces are unbalanced if the net force is not zero. The object must be accelerating.

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1. Barry pushes a desk to the right with a force of 250 N as Jenna helps him push it to the right with a force of 325 N. What is the net force on the desk? In what direction? Are the forces balanced or unbalanced? Is the desk accelerating? Answer: 250 N + 325 N = 575 N to the right The forces are unbalanced The desk is accelerating

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2.Carrie pulls a book east towards her with a force of 65 N while Martha pulls the book west towards her with a force of 55 N. What is the net force on the book? In what direction? Are the forces balanced or unbalanced? Is the book accelerating? Answer: 65 N - 55 N = 10 N to the east The forces are unbalanced The book is accelerating

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3.Kathy and Beth are arguing where their sofa should go. Kathy pushes the sofa to the right with a force of 175 N while Beth pushes it to the left with a force of 175 N. What is the net force on the desk? In what direction? Are the forces balanced or unbalanced? Is the desk accelerating? Answer: 175 N - 175 N = 0 N, no direction The forces are balanced The desk is not accelerating

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4.Two students pushes a heavy crate each with a force of 225 N north while one student pushes it south with a force of 300 N. What is the net force on the crate? In what direction? Are the forces balanced or unbalanced? Is the crate accelerating? Answer: (225 N x 2) – 300 N 450 N – 300 N = 150 N, north The forces are unbalanced The crate is accelerating

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5.The force of gravity is pulling a pail of water downward with a force of 50 N while a rope is holding it up with a force of 50 N. What is the net force on the pail? In what direction? Are the forces balanced or unbalanced? Is the pail accelerating? Answer: 50 N – 50 N = 0 N, no direction The forces are balanced The crate is not accelerating

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