1. Intro To Forces Day!

2. Force Demonstration Volunteers? Have one force push to the right.
Have one force push to the left.
Have 2 forces push to the right.
Have 2 forces push to the left.
Have 2 forces push in opposite directions on the same object.
Have 2 forces push to the right and 1 force push to the left.
Have 1 force push to the right and 3 forces push to the left.
Volunteers?

3. Force - a push or pull on an object
A force can change the direction of an object.
Scientists express force using a unit called the Newton (N). One Newton of force is the amount needed to accelerate a mass 1kg in size 1.0 m/s/s.
Forces affect how objects move.

4. Motion is any physical movement or change in position or place.
The starting point you use to describe the motion of an object is called the reference point.
While using a reference point to describe motion, you will also need to state the direction of the movement.
Direction may be up or down, right or left, north or south, east or west, etc.

5. PRACTICE Describe the force needed to put each object in motion.
Balloon – Need to let the balloon go
Paddle – Need to move the paddle up and down to make the ball move
Swing – Need to use feet to push off of the ground
Soccer ball – Need to kick the ball

6. Net Force is the combination of ALL the forces acting on an object
Net Force is the combination of ALL the forces acting on an object. The Net Force is dependent upon the direction of the forces.
Balanced Forces = NO Motion
The net force = Zero
Unbalanced Forces = MOTION
The net force = SUM of the two forces

7. When two unequal forces act in opposite directions on an object, the net force is the difference of the two forces. The final force and its direction are called a resultant.

8. 1. The forces shown above are PUSHING / PULLING forces.
2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.
3. The forces are EQUAL / NOT EQUAL.
4. The forces DO / DO NOT balance each other.
5. The resultant force is 1000 N TO THE RIGHT / 1000 N TO THE LEFT / ZERO.
6. There IS / IS NO motion.
Practice

9. Answers: 1. The forces shown above are PUSHING / PULLING forces.
2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.
3. The forces are EQUAL / NOT EQUAL.
4. The forces DO / DO NOT balance each other.
5. The resultant force is 1000 N TO THE RIGHT / 1000 N TO THE LEFT /ZERO.
6. There IS / IS NO motion.

10. 1. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.
2. The forces are EQUAL / NOT EQUAL.
3. The forces DO / DO NOT balance each other.
4. The stronger force is pulling to the RIGHT / LEFT.
5. The weaker force is pulling to the RIGHT / LEFT.
6. Motion is to the RIGHT / LEFT.
Practice

11. Answers:
1. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.
2. The forces are EQUAL / NOT EQUAL.
3. The forces DO / DO NOT balance each other.
4. The stronger force is pulling to the RIGHT / LEFT.
5. The weaker force is pulling to the RIGHT / LEFT.
6. Motion is to the RIGHT / LEFT.

12. Forces Acting on Objects
Depending on the situation, there will be certain forces acting upon an object.
Here are a few forces that we will be using for this unit:
Normal Force: The support force applied to an object that is in contact with another stable object.
Gravity Force: The force with which the earth, moon, or other massively large object attracts another object towards itself. Gravity will always be a force acting on an object.
Air Resistance: A special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object.

13. Vectors
Despicable Me Clip:
A vector shows the direction and the magnitude (amount) of a force.
It is a line with an arrow and begins with a dot.
The length of the arrow shows the amount of force.
The arrow shows the direction of the force.
Each square represents 1 N.

14. Force Diagrams
A science book is at rest on a table top. Diagram the forces acting on the science book.
A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting on the skydiver.
Two teams are competing in a tug-of-war contest. Team A is pulling at 4000N and Team B is pulling at 4900N is the opposite direction. Sketch the forces and show the net force exerted. Which team is winning? Is this force balanced or unbalanced?
Tommy and John are trying to move a large table. John pushes with a force of 1150N and Tommy helps him by pushing on the same side of the table with a force of 800N. Sketch the individual forces exerted on the table and then calculate and show the net force exerted on the table.
Practice
Go over the first one together than have them work on the last 3 in table groups. Have one student come up to the whiteboard and have them draw their force diagram, but have them check with you first.

15. A science book is at rest on a table top
A science book is at rest on a table top. Diagram the forces acting on the science book.

16. A skydiver is descending with a constant velocity
A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting on the skydiver.

17. Two teams are competing in a tug-of-war contest
Two teams are competing in a tug-of-war contest. Team A is pulling at 4000N and Team B is pulling at 4900N is the opposite direction. Sketch the forces and show the net force exerted. Which team is winning? Is this force balanced or unbalanced?

18. Tommy and John are trying to move a large table
Tommy and John are trying to move a large table. John pushes with a force of 1150N and Tommy helps him by pushing on the same side of the table with a force of 800N. Sketch the individual forces exerted on the table and then calculate and show the net force exerted on the table.

19. Calculating Net Force Examples
An object has 2 forces pushing on the left. One force is 30 N and the other force is 15 N. What is the net force? Is it balanced or unbalanced? What direction is the object moving?
An object has a force of 10 N pushing from the left and 2 forces (15 N and 5 N) pushing from the right. What is the net force? Is it balanced or unbalanced? What direction is the object moving?
1) 30 N + 15 N = 45 N to the right
2) 10 N left and 20 N to the right  Net Force = 20 – 10 = 10 N to the right and it’s unbalanced

20. Mini Discussion
What do you think the activity in the beginning of class was demonstrating?
Net Forces and the different forces acting on an object with resulting movements