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PHY183-Lecture11pre

# 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 = − F g ˆ y F 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!), mg , is measured in units of N Weight and Mass

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