Ch. 4 Forces

Objectives Develop and interpret free-body diagrams. Calculate and describe the affect of forces on objects. Understand the relationship between force and acceleration.

Forces Force – the interaction of an object with its environment A push or a pull Agent – source of force

Forces Can change an object’s velocity by increasing or decreasing acceleration Can change an object’s direction

Forces SI unit is the Newton (the amount of force that when acting on a 1 kg mass, produces an acceleration of 1 m/s2) 1 N = 1kg•m s2

Forces Two categories of forces Contact Force Field Force

Contact Force Involve contact between two or more objects ex. You hit a ball

Field Force Does not involve contact between two objects Ex. Magnetic field – attraction or repulsion between magnetic objects

Field Force The presence of an object affects the space around it. A force is exerted on any other object within that space

Field Force The region of influence is called a field Objects exert forces on each other when their fields interact

Force Diagrams Force is a vector The effect of force depends on both the magnitude and direction Net forces – all forces acting on an object Balanced and unbalanced forces

Force Diagrams Forces are represented by arrows The arrow is drawn from the center of the object

Force Diagram Called a Free Body Diagram The object the forces are acting on is removed from it’s environment Normal Force opposes the Gravitational Force Frictional Force opposes the Applied Force

Free Body Diagram Normal Force (FN) Applied Force (Fa) Frictional Force (Fs or Fk) Gravitational Force (Fg)

What is Net Force? F1 When more than one force acts on a body, the net force (resultant force) is the vector combination of all the forces, i.e., the “net effect.” F2 F3 Fnet

A tow truck is exerting a force of 5800 N on a car A tow truck is exerting a force of 5800 N on a car. The gravitational force on the car is 14,700 N directed toward the center of the Earth. The Earth directs a force of 13,690 N on the car. The road exerts a backward friction force of 775 N on the car. Draw a free-body diagram of the forces on the car.

5800 N

5800 N 14700 N

13690 N 5800 N 14700 N

13690 N 5800 N 775 N 14700 N

13690 N = FN Fa= 5800 N 775 N = Fs 14700 N = Fg