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## FORCES

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**Which vehicle exerts a greater force ― the tow truck or**the car? ISP 209 - 2B**What is a force?**• A push or a pull • When one object pushes or pulls another object, you say that the first object exerts a force on the second object. • Let’s practice. What forces are at play around you?**What forces are exerted?**Playing catch with a medicine ball**Playing catch with a medicine ball**A B A throws the ball and B catches it. four forces When A throws the ball he exerts a force on the ball (toward the right) and the ball exerts a force on him so he recoils (toward the left). When B catches the ball he exerts a force on the ball (toward the left to stop it) and the ball exerts a force on him so he is knocked back (toward the right). ISP 209 - 2B**Let’s take a minute to discuss….**Scalars and Vectors • Are both quantities • BUT….. • Scalars are fully described by magnitude (magnitude= number) • Vectors are fully described by both magnitude(number) and direction**What is force categorized as?**• Force is described by the strength and direction in which it acts. • Therefore, • Force is a VECTOR**The strength of force is measured in…**• The SI unit called the Newton (N) • One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. • Thus, the following unit equivalency can be stated:**Combining Forces**• Often, more than one force acts on an object at a time. • Net force is the combination of all forces acting on the object • What does the net force determine? • Motion • direction**Net force Practice**• For each diagram, write the net force and direction. HINT: The net force always acts in the direction of the greater force.**Balanced forces**• Equal forces acting on one object in opposite directions.**Balanced Forces**• Balanced forces result in equilibrium • How can I make this box in equilibrium?**Unbalanced Forces**• Unbalanced forces result when the forces exerted on an object are not equal. • Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.**Free-Body Diagrams**• Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.**Draw a free body diagram**• A physics book is sitting on a table and is pushed 10 N to the right. The opposing frictional force is 7 N.**The horse pulls the cart with a force A (to the right).**According to Newton, the cart pulls the horse with a force –A (to the left). A puzzle Horse and Cart So how can they start moving, or accelerate? Resolution: Consider each part separately, and don’t forget that there are other forces acting. ISP 209 - 2B**Homework**• Read Introduction of Forces notes • Give 3 examples of force for each of the following: (YOUR OWN EXAMPLES!) • Gravity • Tension • Friction • Drag/Air resistance