Net Forces

In this PPT… Yellow text should be recorded in your Physics Notebook. All other text is not required, but you may choose what to record in your notebook.

Force Force is defined as a push or a pull on an object

Force Forces can cause objects to: o Start moving o Stop moving o Change direction A force is described by its strength and by the direction in which it acts. Direction: represented by an arrow Strength: determined by length of arrow Longer the arrow, the greater the force

Force Example Which person is applying more force to the object? Are they pushing or pulling?

The unit for force is the Newton (N) Named after Isaac Newton Newton = kgm/s/s 1N is the amount of force it takes to move a 1 kg mass 1 meter every second A spring scale is used to measure force in Newtons.

Net Force Net Force: total force felt by an object All individual forces COMBINE together If the net force is 0N, the object does not change its motion. Forces are balanced. If the net force is greater than 0N, the object changes its motion. Forces are unbalanced.

NET FORCE Net Force : total force felt by an object All individual forces add together  Tells if forces are balanced or unbalanced  Ex:25N  + 20N  = 45N  12N  + 10N  = 2N  **Think adding positive & negative integers

Balanced Forces Balance forces do not change an object’s motion. Net Force = 0 N –RESULT: Object does not move OR –RESULT: Object stays at constant speed

Balanced Forces How much force is each person applying to the box?

Balanced Forces Turn and Talk: Come up with an example of balanced forces where an object is in motion.

Unbalanced Forces Net Force = NOT ZERO Unbalanced forces change an object’s motion –RESULT: Object moves Or –RESULT: Object changes speed Or –RESULT: Object changes direction

Example What is the net force in this system? How do you know? Are the forces balanced or unbalanced?

Rocket Sled Demonstration

Tug the Table Does this online game sound familiar? How does the new knowledge you have gained relate to this game?

Compare and Contrast Balanced vs. Unbalanced Force CharacteristicBalanced ForceUnbalanced Force Net Force0 NewtonsGreater than 0 Newtons Affect on MotionDoes not change the object’s motion Causes the object to accelerate -speed increase -speed decrease -change in direction.

Net Force Example Figure 1: Net forces are balanced. Net force= 0 N Figure 2: Net forces are unbalanced. Net force= 400 N left – 300 N right 100 N left

Net Force Example

Videos Video 1 Calculating Net Force