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Motion and Force. Chapter Four: Forces. 4.1 May the Force Be With You. 4.1 The cause of forces. A 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. 4.1 How do you measure force?.
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Chapter Four: Forces • 4.1 May the Force Be With You
4.1 The cause of forces • A 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.
4.1 How do you measure force? • The conventional unit for measuring force is in pounds • For example: • A lion bites down with 1,235 pounds of bite force • A boxer can deliver 2,350 pounds of force with a single punch
4.1 Metric Units of Force • Thenewton(N) is a metric unit of force. • One pound of force equals 4.45 newtons. Examples: • A lion bites down with 5,533 N of force • A boxer can punch with 10,528 N of force
4.1 Gravity and weight • The force of gravity on an object is called weight. • Mass and weight are not the same thing!
Remember….g = 9.8 An elephant has a mass of 6,800 kg. What is his weight in Newtons?
4.1 Gravity and weight • A 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.
g (moon) = 1.68 • So….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?
4.1 Addition of vectors • It is sometimes helpful to show the strength and direction of a force using an arrow. • This arrow is known as a FORCE VECTOR If 1 cm = 1 N, how many newtons of force does this line represent?
4.1 The force vector • A 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.
4.3 Adding forces • The 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?
4.3 Adding forces • To 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: • weight • drag (air friction) • the thrust of the engines, and • the lift force caused by the flow of air over the wings.
4.3 Balanced & Unbalanced Forces When several forces act on the same object: • The net force is zero, or • The net force is NOT zero. Which of these situations will result in the box moving?
Balanced 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?
4.3 Equilibrium and normal forces • A normal force is created whenever an object is in contact with a surface. It is also known as support force • The normal/support has equal strengthto the object’s weight.
4.3 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?
4.1 Forces in springs and ropes • Tensionis 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?
4.1 Forces in springs and ropes • When you apply a compressionforce 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.
Review Questions • Page 86 – 2,3,4,5 and 8 • Page 99 - 1,2,3,4,6 and 7