PHY183-Lecture11pre - Types of Forces Contact force Physics...

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1 January 31, 2012 Physics for Scientists&Engineers 1 1 Physics for Scientists & Engineers 1 Spring Semester 2012 Lecture 11 Force Types of Forces Contact force Tension Compression Normal force (perpendicular) Friction force Spring force A force is needed to stretch or compress a spring Has the special property that it depends linearly on the change in length of the spring January 31, 2012 Physics for Scientists&Engineers 1 2 Fundamental Forces All the forces on the previous slide are manifestations of the four fundamental forces Gravitational force • When you hold an object in the air and release it, it falls to the ground Electromagnetic force • Repulsion of like electric charges • Attraction of opposite magnetic poles Strong nuclear force • Holds atomic nuclei together Weak nuclear force • Responsible for the decay the neutron January 31, 2012 Physics for Scientists&Engineers 1 3 Don't affect our everyday lives Gravitational Force Vector Forces have a direction If you hold a laptop in your hand, you can tell that the gravitational force points downward (- y direction) January 31, 2012 Physics for Scientists&Engineers 1 4 F g =− g ˆ g = mg January 31, 2012 Physics for Scientists&Engineers 1 5 Weight and Mass Magnitude of gravitational force on an object = weight Gravitational force on an object, F g , is always proportional to its mass Near surface of Earth (altitude of 10 km or less): Weight is constant and is the product of object’s mass and the Earth’s gravitational acceleration: g = 9.81 m/s 2 January 31, 2012 Physics for Scientists&Engineers 1 6 Example: Object with mass m = 5.00 kg Gravitational force F g = mg = (5.00 kg)(9.81 m/s 2 ) = 49.05 kg m/s 2 Force Unit 1 kg m/s 2 = 1 N Named after British physicist Sir Isaac Newton (1642- 1727), father of modern mechanics and perhaps the most influential scientist who ever lived Summary: mass, m , is measured in units of kg whereas weight (a force!), , is measured in units of N Weight and Mass
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2 Orders of Magnitude of Forces January 31, 2012 Physics for Scientists&Engineers 1 7 Force to stretch DNA Force to hold single electron in hydrogen atom Force of air on eardrum Human body weight Force of Earth’s atmosphere Weight of water behind a dam Force of Sun’s gravity on Earth January 31, 2012 Physics for Scientists&Engineers 1 8 Net Force Definition: Net force = vector sum of all forces acting on a given object Cartesian components of net force are given by: F net = F i i = 1 n = F 1 + F 2 + ... + F n F net, x = F i , x i = 1 n = F 1, x + F 2, x + ... + F n , x F net, y = F i , y i = 1 n = F 1, y + F y + ... + F n , y F net, z = F i , z i = 1 n = F 1, z + F z + ... + F n , z
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This note was uploaded on 04/02/2012 for the course PHY 183 taught by Professor Wolf during the Spring '08 term at Michigan State University.

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PHY183-Lecture11pre - Types of Forces Contact force Physics...

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