FORCES Which vehicle exerts a greater force the

FORCES

Which vehicle exerts a greater force ― the tow truck or the car? 9/7/2006 ISP 209 - 2 B 2

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?

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). 9/7/2006 ISP 209 - 2 B 6

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

QUANTITY 5 m 30 m/sec, East 5 mi. , North 20 Degrees Celsius 256 bytes 4000 calories SCALAR or VECTOR?

QUANTITY SCALAR or VECTOR? 5 m Scalar 30 m/sec, East Vector 5 mi. , North Vector 20 Degrees Celsius Scalar 256 bytes Scalar 4000 calories Scalar

What is force categorized as? • Force is described by the strength and direction in which it acts. • Therefore, • Force is a

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.

A puzzle Horse and Cart 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). So how can they start moving, or accelerate? Resolution: Consider each part separately, and don’t forget that there are other forces acting. 9/7/2006 ISP 209 - 2 B 19

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