Phys101_chap5.pdf

# Phys101_chap5.pdf - Physics 101 Prof Ekey Chapter 5 Force...

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Physics 101 Prof. Ekey Chapter 5 Force and motion (Newton, vectors and causing commotion) “Goal of chapter 5 is to establish a connection between force and motion” This should feel like chapter 1 Questions A force… (a) always produces motion (b) is a scalar quantity (c) is capable of producing a change in motion (d) both a and b. If the net force on an object is zero, the object could… (a) be at rest (b) be in motion with a constant velocity (c) have zero acceleration (d) all of the above

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Rope = agent Spring = agent Earth = agent Force of rope on box Pull Force of spring on box Push Force of gravity on box Pull – Long range What is a force? A force is a push or pull acting on an object. Specific action(s). A force is a vector. It has a magnitude and direction. A force requires an agent. Something does the pushing or pulling. A force is either a contact force or a long-range force. Touching Gravity (and others) “In the particle model, an object cannot exert a force on itself. A force on an object will always have an agent (cause) external to the object.” We’re ignoring internal forces for now. (magnitude & direction) Force – Vector Units : Newton (kg m/s 2 ) Forces can produce a change in motion. - start/stop an object in motion - change velocity of an object (acceleration) - could have no effect on an object’s motion Net force, F net = Superposition of forces. Look at combined effect of all forces on an object. Sum (resultant) of all forces on an object F net = F i = F 1 + F 2 + F 3 + F 4 ... Note we can decompose these into components F net , x = F i , x and F net , y = F i , y Recall chapter 3, trig and soh, cah toa. Equilibrium = “no motion” & Net force of Zero
George and Jill pull on opposite sides of a 100kg box . Why? +x + =0? + = What happens to the box? F George =5.0 N F Jill Are other forces acting on the box? Example If George pulls with 5.0 N, what force does Jill have to pull with to make the box stay stationary? What if Jill pulls with -3.0 N? Net force? 100 kg Question Two of three forces are shown.

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