* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Constant Force
Coriolis force wikipedia , lookup
Frictional contact mechanics wikipedia , lookup
Classical mechanics wikipedia , lookup
Equations of motion wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Jerk (physics) wikipedia , lookup
Fundamental interaction wikipedia , lookup
Fictitious force wikipedia , lookup
Newton's theorem of revolving orbits wikipedia , lookup
Centrifugal force wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Mass versus weight wikipedia , lookup
Centripetal force wikipedia , lookup
Lecture PowerPoints Chapters 2, 3.1, 4, 5.10 Physics: Principles with Applications, 6th edition Giancoli © 2005 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Constant Force Apply Newton’s Second Law • Force and Acceleration • Types of Forces • Equilibrium • Analyze Friction Constant Force Newton’s Second Law • In an inertial reference frame, the sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object F = ma. Where: F is force in newtons m is mass in kilograms a is acceleration in m/s2 Constant Force Newton’s Second Law • Another way to state this is that if you apply an unbalanced force to an object with mass, it will accelerate in the direction of the applied force Constant Force Newton’s Second Law • Relationships between acceleration, force and mass • Rewrite F = ma to solve for a • F/m = a • So force is directly proportional to acceleration (for the same mass, more force = more acceleration) • And mass is inversely proportional to acceleration (for the same force, more mass means less acceleration) Constant Force Newton’s Second Law • Types of forces (review) –Field force • Includes gravitational, electromagnetic –Contact force • Includes normal, tension, friction Constant Force Newton’s Second Law • Equilibrium –When net force on an object is zero –Σ =0 • Nonequilibrium •Σ =ma Constant Force Friction Exists between two solid surfaces because even the smoothest surface is quite rough on a microscopic scale. The vector friction is always opposite the direction of the applied force or motion Constant Force Types of friction: If no motion occurs, referred to as static friction Example: You push on a refrigerator, and it finally starts to move. Static friction kept it from moving Constant Force Types of friction: If motion occurs, referred to as kinetic (sliding) friction Example: You let go of the moving refrigerator, and it starts to slow down then stops due to sliding friction Constant Force Types of friction: When object rolls on surface, referred to as rolling resistance Example: One reason your bicycle slows if you stop pedaling Constant Force Types of friction: Air resistance opposes the motion of objects moving in air (examples: open parachute, sail on sailboat) Terminal velocity* is highest velocity attainable by an object as it falls through a fluid (gas or liquid). At terminal velocity, resistance = weight of object. Terminal velocity in air for a skydiver in freefall is 195 km/h (122 mph or 54 m/s). *Source: https://en.wikipedia.org/wiki/Terminal_velocity Constant Force What causes friction? • Surfaces are not smooth even if they appear to be (microscope) • Dry friction (static friction and sliding friction) arises from a combination of – – – – Inter-surface adhesion Surface roughness Surface deformation Surface contamination Constant Force Friction Coefficient of static friction (μs) If you know Fs, you know only one of the infinitely many possible static frictional forces that could be exerted between the two bodies. Which force do you know? The maximum static frictional force. Constant Force Friction Coefficient of kinetic (sliding) friction (μk) The amount of kinetic friction Fk a body experiences is proportional to the size of the normal force N exerted on the body by the structure it slides against. Constant Force Friction Coefficient of kinetic (sliding) friction (μk) Note: The statement “kinetic friction is a function of normal force only-- surface area has nothing to do with it” is true ONLY as long as you are dealing with two rigid bodies that are sliding relative to one another.