6 1 Force and Motion Force and Motion

6 -1 Force and Motion

Force and Motion �An object that experiences a push or pull has experienced a force exerted on it �The object is called the System �The world around it is called the Environment �Force is represented by F �Force is a vector �Examples? ? ?

Forces �Forces by the environment can be divided into two types �Contact Force �Acts on object by touching it �Long-Range Force �Force exerted without contact �Magnets, Gravity

Pictorials and Agents �Each force has a specific and measurable cause called Agent �On your book � Desk holding it up � Gravity holding it down �Drawing a picture will help solve problems �Object replaced by a dot with arrows showing the forces on it �Arrow tail is always placed on the dot

Draw Pictorial Models �A book held in your hand �A book Pushed across by your hand

Newton’s 2 nd Law �While conducting experiments, try to eliminate friction and influence of gravity �Newton’s 2 nd Law �Force and acceleration are proportional �Larger the force, the greater the acceleration �Acceleration = Net force / Mass �a = Fnet / m �Use a free body diagram to determine all forces acting upon an object

Combining Forces �Using vector addition, you can graphically see forces being combined �Use kinematics to find velocity and position of the object �An unbalanced force causes a change in velocity F 1 F 2 Fnet

Measuring Force �One unit of force causes a 1 -kg mass to accelerate as 1 m/s 2 �F = ma �Unit is the Newton (N) = km x m/s 2 �An object has an acceleration in a horizontal direction of 2. 50 m/s 2 with a mass of 4. 60 kg. How much force does the object have? �m = 4. 60 kg accel = 2. 50 m/s 2 �F = ma F = (4. 60 kg)(2. 50 m/s 2) �F = 11. 5 N in the horizontal direction

Newton’s 1 st Law �Galileo did many experiments on motion �He concluded that horizontal motion was eternal �Newton generalized Galileo’s results of motion � 1 st Law �Object at rest will remain at rest or object in motion will continue to move in a straight line with constant speed if the net force acting on that object is zero

Newton’s 1 st Law �Inertia �Tendency of an object to resist change �Equilibrium �If net force on an object is zero, object at equilibrium �Object either at rest, or moving at constant speed �A change in velocity is the result of a net force acting on object

Sample of Forces

Free body diagrams �Net force on an object causes acceleration �Important to know how to find the Net force �Draw a Free Body Diagram �A rope is lifting a heavy bucket. The speed of the bucket is increasing. How can the force on bucket be related to change in speed?