2Chapter Four: Forces4.1 May the Force Be With You
34.1 The cause of forcesA force is a push or pull, or any action that has the ability to create change.The key word here is action, force is an action.
44.1 How do you measure force? The conventional unit for measuring force is in poundsFor example:A lion bites down with 1,235 pounds of bite forceA boxer can deliver 2,350 pounds of force with a single punch
54.1 Metric Units of Force The newton (N) is a metric unit of force. One pound of force equals 4.48 newtons.Examples:A lion bites down with 5,533 N of forceA boxer can punch with 10,528 N of force
64.1 Gravity and weightThe force of gravity on an object is called weight.Mass and weight are not the same thing!
7Remember….g = 9.8An elephant has a mass of 6,800 kg. What is his weight in Newtons?
84.1 Gravity and weightA 10-kilogram rock has a mass of 10 kilograms no matter where it is in the universe.A 10-kilogram rock’s weight however, can vary greatly depending on where it is.
9g (moon) = 1.68So….has the MASS of the elephant changed, just because he is on the moon?What is his new WEIGHT due to the difference in gravity?
104.1 Addition of vectorsIt is sometimes helpful to show the strength and direction of a force using an arrow.This arrow is known as a FORCE VECTORIf 1 cm = 1 N, how many newtons of force does this line represent?
114.1 The force vectorA force vector has units of newtons, just like all forces.Forces can be added together to determine what motion an object will have.Positive and negative numbers indicate opposite directions.
124.3 Adding forcesThe sum of all the forces on an object is called the net force.The word net means total but also means the direction of the forces has been taken into account.In what direction will this plane go?
134.3 Adding forcesTo figure out if or how an object will move, we look at ALL of the forces acting on it.Four forces act on a plane:weightdrag (air friction)the thrust of the engines, andthe lift force caused by the flow of air over the wings.
154.3 Balanced & Unbalanced Forces When several forces act on the same object:The net force is zero, orThe net force is NOT zero.Which of these situations will result in the box moving?
16Balanced Forces When the forces are balanced, the net force is zero. When the net force on an object is zero, we say the object is in equilibrium.What force is acting to push the book down?
174.3 Equilibrium and normal forces A normal force is created whenever an object is in contact with a surface. It is also known as support forceThe normal/support has equal strength to the object’s weight.
184.3 Solving equilibrium problems For an object to be in equilibrium, all the forces acting on the object must add up to zero.Is this object in equilibrium?
194.1 Forces in springs and ropes Tension is a force that acts in a rope, string, or other object that is pulled.Tension always acts along the direction of the rope.In what direction will each boy go?
204.1 Forces in springs and ropes When you apply a compression force to a spring, it collapses to become shorter.The force created by stretching or compressing a spring always acts to return the spring to its natural length.
21Review QuestionsPage 86 – 2,3,4,5 and 8Page ,2,3,4,6 and 7