Balanced and Unbalanced Forces SC. 6. P. 13 Balanced and Unbalanced Forces SC.6.P.13.3 Investigate and describe that an unbalanced force acting on an object changes its speed, or direction of motion, or both. ALSO ASSESSES: SC.6.P.12.1 Measure and graph distance versus time for an object moving at a constant speed. Interpret this relationship. Essential Question: How do forces cause an object to change its motion and/or speed?

Video: :Measuring the Motion of an Object”

Bell Ringer Cesar and Jill went to a field to play soccer. As the ball rolled downward toward Jill, she used her foot to kick the ball and keep it in play. Cesar realized he could apply scientific principles to a soccer game. Which of the following best describes the scientific principle that Cesar observes as Jill kicks the ball? An unbalanced force has no effect on the ball. Gravity on the ball is equal to the force of friction. A net force of zero changes the direction of the ball. Unbalanced forces change the ball’s speed and the direction of motion.

Interactive Journal: “I DO”

Net Force Net force is the total of all forces acting on an object. If the net force is zero, the forces are balanced and the object is holding still. If the net force is not zero, the forces are unbalanced and the object is in motion.

Balanced vs. Unbalanced Balanced forces- When two or more forces acting on an object are equal in all directions. Results in no movement Unbalanced forces- When two or more unequal forces act on an object. Moves in the direction with more force. Net force is the difference between these forces.

Unbalanced Force Example #1 50 N to the right. Which direction will the ball move and with how much force?

Net Force Example #2: What is the net force on the airplane? The airplane is moving with a force of 800 N. However, there are two forces moving in opposite directions on the airplane. Just add these two forces: 40 N  + 60 N = 100 N Subtract to get the net force: 800 N  - 100 N  = 700 N The net force is 700 N. The airplane will move with a force of 700 N as a result of air friction and wind. 

Changing Speed and/or Direction of Motion When two people collide in football, would their speed or direction of motion change? Both! A collision slows down moving objects and often changes their direction.

Distance vs Time Graphs Origin: The starting location in a distance vs time graph. Moving away from origin. Returning to Origin Origin

Positive and Negative Acceleration Positive Acceleration: When an object increases its speed. (speeds up) Negative Acceleration: When an object decreases its speed. (slows down) Negative Acceleration 25 km/h 50 km/h

Distance vs. Time Graph Example Tao is drawing a graph that shows four different objects and the distance each object traveled in a 5 second period. Which line on the graph shows the object that is traveling with the fastest constant speed? Line A Line B Line C Line D This portion of the FCIM lesson is connected to the “daughter” benchmark – Sc.6.P.12.1 Measure and graph distance versus time for an object moving at a constant speed. Interpret this relationship. Note: According to the DOE’s Content Focus Report for the Science FCAT 2012, 2013, 2014, students were expected to respond to questions based on the this benchmark. Correct Answer: B

Interpreting Distance vs Time Graphs “We DO” Together 1. What is happening between B and C? 2. Is the person moving faster during line segment AB or line segment CD? 3. What is the person doing between E and F? Holding still Line segment CD, because it has a steeper slope. Retuning to origin at a steady speed.

“We DO” Reading Distance vs Time Graphs

Revisit Bell Ringer Cesar and Jill went to a field to play soccer. As the ball downward toward Jill, Jill used her foot to kick the ball and keep it in play. Cesar realized he could apply scientific principles to a soccer game. Which of the following best describes the scientific principle that Cesar observes as Jill kicks the ball? An unbalanced force has no effect on the ball. Gravity on the ball is equal to the force of friction. A net force of zero changes the direction of the ball. Unbalanced forces change the ball’s speed and the direction of motion.*

YOU DO TIME!

YOU DO QUESTION #1 Correct Answer: B

YOU DO QUESTION #2 John left his home and walked 3 blocks to his school, as shown in the accompanying graph. What is one possible interpretation of the section in the graph from point B to point C? John arrived at school and stayed throughout the day. John waited before crossing a busy street. John returned home to get his math homework. John reached the top of a hill and began walking on level ground. Correct Answer: B

YOU DO QUESTION #3 Dominique and her sister are practicing their basketball skills at the park. If both Dominique and her sister both throw their basketballs at the same time and they hit each other. What would happen to their basketballs?   Only the basketball’s speed would be changed Only the basketball’s directions would be changed Both the basketball’s speed and direction would change Neither the basketball’s speed nor direction would change Correct Answer: C

Exit Slip Marie left her briefcase at home. State which point represents when she turned back around to go home. Explain how you arrived at this conclusion. Correct Answer: C