Balanced, Unbalanced & Net Forces Created by Kesler Science – More 5E lessons at KeslerScience.com Presented by Kesler Science

Essential Questions: What are balanced and unbalanced forces? How do unbalanced forces cause a change in position, direction, and speed of an object when acted upon by unbalanced forces? What are ways to demonstrate how unbalance forces change the speed or direction of an object’s motion? What are ways to calculate how unbalanced forces change the speed or direction of an object’s motion?

Balanced and Unbalanced Forces A push or a pull that causes an object to stop, move, or change direction. Forces push downward toward the Earth’s center (gravity) or push upward on an object (normal or supporting force). Forces may or may not cause movement. Ex. 1 – A book pushes down on a table while the table pushes up on the book. Ex. 2 – A car accelerates(changes speed and direction)causing motion. © KeslerScience.com

Forces Template Quick Action – Forces INB Template Cut out the Balanced, Unbalanced, Net Force template. Fold along the dashed lines. Glue it to your journal (page 31) along the skinny tab. Define each term. © KeslerScience.com

Balanced and Unbalanced Forces Two forces equal in size and acting in opposite directions on an object. The object stays still or continues to move at the same (constant) speed and in the same direction. Students understand the concept of balanced forces being at rest, but struggle to grasp the concept that forces are balanced if the object continues moving at the same speed and in the same direction. © KeslerScience.com

Balanced Forces Examples Balanced and Unbalanced Forces Balanced Forces Examples At rest At rest At rest At a constant speed and same direction At a constant speed and same direction © KeslerScience.com

Unbalanced Forces Balanced and Unbalanced Forces Always cause a Two forces that are unequal in size and opposite in direction. Always cause a change in motion in one of these areas: position direction speed © KeslerScience.com

Unbalanced Forces Examples Balanced and Unbalanced Forces Unbalanced Forces Examples Horse #2 is stronger 20N Moves Left 10N The student exerting the strongest force will determine the direction of movement. Changing directions © KeslerScience.com

Quick Action – Demonstrate Forces Choose a partner for this activity. The teacher will number off the pairs. Even numbered pairs will come up with an example of a balanced force, which they will present to the class. 3. Odd numbered pairs will come up with an example of a unbalanced force, which they will present to the class. (Use examples of changing either position, speed or direction) © KeslerScience.com

Quick Action – Balanced or Unbalanced Template Cut out the template Fold the flaps away from the side that says “Glue this side down” Glue it to your journal (page 31) on the hexagon side that says “Glue this side down” Answer “balanced” or “unbalanced” under each flap. © KeslerScience.com

Balanced and Unbalanced Forces How do unbalanced forces cause a change in position of an object? A skier is at the top of a hill (balanced force). Another skier bumps him (unbalanced force) causing him to fall down. This unbalanced forced caused his position to change.   © KeslerScience.com

Balanced and Unbalanced Forces How do unbalanced forces cause a change in direction of an object? A skier is at the top of a hill (balanced force). Then then the skier decides to point her skis down the hill and push off (unbalanced force). This unbalanced force causes her a change in direction.   © KeslerScience.com

Balanced and Unbalanced Forces How do unbalanced forces cause a change in speed of an object? A skier is at the top of a hill (balanced force) at the beginning of a race. As he flies down the mountain (unbalanced force) he picks up speed. This unbalanced force causes him a change in speed.   © KeslerScience.com

Check for Understanding Can you… 1. Describe balanced and unbalanced forces? 2. Identify and describe how unbalanced forces cause a change in position, direction, and speed of an object when acted upon by unbalanced forces? Clear up any confusion and answer questions. © KeslerScience.com

- + Net Force The overall forces acting on an object. Net Forces Net Force  The overall forces acting on an object. Measured in Newtons (N) + - © KeslerScience.com

Quick Action – Let’s Practice Choose a partner for this activity. Work together to solve the net force problems on the next four slides. Think about whether you would add or subtract the forces. 3. We will discuss the answer after each slide. © KeslerScience.com

Quick Action – Let’s Practice Without considering other forces such as friction what is the net force in this problem? Which direction will the box move? 50N 30N Answer 80N. If the force is going the same directions, add. The movement is to the right. Unbalanced force. © KeslerScience.com

Quick Action – Let’s Practice Without considering other forces such as friction what is the net force in this problem? Which direction will the box move? 20N 30N Answer 10N. If the force is going in opposite directions, subtract. The movement is to the right. Unbalanced force. © KeslerScience.com

Quick Action – Let’s Practice Without considering other forces such as friction what is the net force in this problem? Which direction will the box move? 10N 5N 20N Answer 25N. If the force is going the same directions, add. The force on the right needs to be subtracted. The movement is to the left. Unbalanced force. © KeslerScience.com

Quick Action – Let’s Practice Without considering other forces such as friction what is the net force in this problem? What direction will the box move? 20N 20N Answer 0N. The object will be at rest. Balanced force. © KeslerScience.com

Quick Action – Net Force INB Template Checking for Understanding – Individual Practice Cut out the INB template and also cut on the lines between the diagrams up to the dotted line. Fold on the dotted line and paste into your notebook (page 32). Lift up the flap and work the problem. Also, draw an arrow indicting the direction of the movement. Copy the notes below and write them somewhere on this INB page. Subtract (opposite) Add (same way) © KeslerScience.com

Calculating Net Force Examples Quick Action – Net Force INB Template Calculating Net Force Examples © KeslerScience.com

Check for Understanding Can you… Demonstrate how unbalance forces change the speed or direction of an object’s motion? Calculate how unbalanced forces change the speed or direction of an object’s motion? Homework: Staple on 32 and complete! Clear up any confusion and answer questions. © KeslerScience.com