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 2nd Law While conducting experiments, try to eliminate friction and influence of gravity Newton’s 2nd 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 F1 F2 Fnet F2 F1 Fnet F1 Fnet F2

Measuring Force One unit of force causes a 1-kg mass to accelerate as 1 m/s2 F = ma Unit is the Newton (N) = km x m/s2 An object has an acceleration in a horizontal direction of 2.50 m/s2 with a mass of 4.60 kg. How much force does the object have? m = 4.60 kg accel = 2.50 m/s2 F = ma F = (4.60 kg)(2.50 m/s2) F = 11.5 N in the horizontal direction

Newton’s 1st Law Galileo did many experiments on motion He concluded that horizontal motion was eternal Newton generalized Galileo’s results of motion 1st 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 1st Law Inertia Equilibrium 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?