Lesson Plan
Push & Pull Power!
Students will be able to differentiate between balanced and unbalanced forces using real-world examples and explain their effects on an object's motion.
Understanding forces helps us explain why things move or stay still around us, from walking to driving. It's fundamental to how the world works!
Audience
7th Grade
Time
30 minutes
Approach
Through discussion, examples, and an interactive activity, students will analyze real-world force scenarios.
Materials
Whiteboard or projector, Markers or pens, Warm Up: Force Facts, Slide Deck: Push & Pull Power!, Activity: Force Scenario Sort, and Cool Down: Balanced or Not?
Prep
Teacher Preparation
15 minutes
- Review the Lesson Plan: Push & Pull Power! and all linked materials.
- Prepare whiteboard or projector for displaying slides.
- Print or prepare to distribute copies of the Warm Up: Force Facts, Activity: Force Scenario Sort, and Cool Down: Balanced or Not? (if using physical copies).
- Ensure access to the Slide Deck: Push & Pull Power! for presentation.
Step 1
Warm-Up: Force Facts
5 minutes
- Distribute the Warm Up: Force Facts worksheet.
- Instruct students to quickly write down anything they remember or know about forces.
- Briefly discuss student responses, activating prior knowledge.
Step 2
Introduction to Forces (Slide Deck)
5 minutes
- Present the Slide Deck: Push & Pull Power! starting from the introduction.
- Define 'force' and introduce the concepts of balanced and unbalanced forces using simple language.
- Emphasize that forces are pushes or pulls.
Step 3
Real-World Examples & Discussion
10 minutes
- Continue with the Slide Deck: Push & Pull Power! to present the real-world examples of balanced and unbalanced forces (e.g., tug-of-war, pushing a car).
- For each example, explain why the forces are balanced or unbalanced and what effect this has on the object's motion.
- Facilitate a brief class discussion, asking students to identify other examples they've observed.
Step 4
Activity: Force Scenario Sort
7 minutes
- Distribute the Activity: Force Scenario Sort.
- Have students work individually or in pairs to classify scenarios as involving balanced or unbalanced forces and explain their reasoning.
- Circulate to provide support and answer questions.
Step 5
Cool Down: Balanced or Not?
3 minutes
- Distribute the Cool Down: Balanced or Not?.
- Students will answer a quick question about a new scenario to demonstrate their understanding of balanced and unbalanced forces.
- Collect the cool-downs as an exit ticket.
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Slide Deck
Push & Pull Power!
Understanding Forces in Action!
Welcome students and introduce the day's topic: forces. Ask students what they already know about pushes and pulls.
What is a Force?
A force is a push or a pull on an object.
Forces can cause objects to:
- Start moving
- Stop moving
- Change speed
- Change direction
- Change shape
Define force as a push or pull. Explain that forces can make things move, stop, or change direction. Ask for examples of pushes and pulls from students' daily lives.
Balanced Forces: No Change in Motion
When forces acting on an object are equal in strength and opposite in direction.
Result: The object's motion does not change.
- If it was still, it stays still.
- If it was moving, it continues to move at a constant speed and in the same direction.
Example: A book resting on a table.
Introduce balanced forces. Emphasize that when forces are balanced, there is no change in motion. Use the example of a book resting on a table. Gravity pulls it down, the table pushes it up, and they balance.
Example: Tug-of-War Stand-off!
Imagine two teams pulling on a rope in a tug-of-war. If neither side is moving, what does that tell you about the forces?
The forces are balanced! Both teams are pulling with equal strength in opposite directions, so the net force is zero.
Present the first real-world example: a tug-of-war that isn't moving. Explain that the forces exerted by both teams are equal and opposite, resulting in no movement of the rope's center.
Unbalanced Forces: Change in Motion
When forces acting on an object are not equal in strength or not opposite in direction.
Result: The object's motion changes.
- It starts moving.
- It speeds up or slows down.
- It changes direction.
Example: Kicking a soccer ball.
Introduce unbalanced forces. Emphasize that when forces are unbalanced, there is a change in motion. Explain that the net force is not zero.
Example: Pushing a Heavy Box!
You try to push a heavy box across the floor. If the box starts to move, what kind of forces are at play?
The forces are unbalanced! Your push is stronger than the friction between the box and the floor, causing the box to accelerate.
Present the second real-world example: pushing a heavy box. Explain that if the box starts moving, your push force is greater than the friction or any opposing force, making the forces unbalanced.
Balanced vs. Unbalanced
Remember:
- Balanced Forces = No change in an object's motion (stays still or constant velocity).
- Unbalanced Forces = Causes a change in an object's motion (starts, stops, speeds up, slows down, changes direction).
Summarize the key difference and open the floor for questions. Reinforce that balanced means no change, unbalanced means change.
Warm Up
Warm Up: Force Facts
Instructions: Take a few minutes to write down everything you already know or remember about forces. What comes to mind when you hear the word "force"?
Bonus: Can you think of a time when you experienced a push or a pull today? Describe it below.
Activity
Activity: Force Scenario Sort
Instructions: Read each scenario below. Decide if the forces acting on the object are Balanced or Unbalanced. Then, explain why you think so and what will happen to the object's motion.
Scenario 1: A car parked on a flat road.
Balanced or Unbalanced?
Why? What happens to the car's motion?
Scenario 2: A soccer player kicking a ball into the goal.
Balanced or Unbalanced?
Why? What happens to the ball's motion?
Scenario 3: A boat floating calmly on still water.
Balanced or Unbalanced?
Why? What happens to the boat's motion?
Scenario 4: A person pulling a heavy sled up a snowy hill.
Balanced or Unbalanced?
Why? What happens to the sled's motion?
Scenario 5: Two people arm wrestling, but neither person's arm is moving.
Balanced or Unbalanced?
Why? What happens to their arms' motion?
Cool Down
Cool Down: Balanced or Not?
Instructions: Read the scenario below and answer the questions.
Scenario:
A skydiver jumps out of a plane. For a few moments, they speed up as they fall. Then, they open their parachute, and their speed quickly decreases until they are floating gently towards the ground at a steady pace.
-
During the first few moments, when the skydiver is speeding up, are the forces acting on them balanced or unbalanced?
-
Explain your reasoning:
-
After the parachute opens and the skydiver is floating gently at a steady pace, are the forces acting on them balanced or unbalanced?
-
Explain your reasoning:
Answer Key
Answer Key: Activity: Force Scenario Sort
Scenario 1: A car parked on a flat road.
Balanced or Unbalanced? Balanced
Why? What happens to the car's motion?
- Reasoning: The force of gravity pulling the car down is equal and opposite to the normal force of the road pushing the car up. There are no other forces acting to cause movement.
- Motion: The car remains still.
Scenario 2: A soccer player kicking a ball into the goal.
Balanced or Unbalanced? Unbalanced
Why? What happens to the ball's motion?
- Reasoning: The force of the player's kick is much greater than any opposing forces (like air resistance or friction with the ground at the moment of impact). This creates a net force in the direction of the kick.
- Motion: The ball accelerates (starts moving, speeds up) in the direction it was kicked.
Scenario 3: A boat floating calmly on still water.
Balanced or Unbalanced? Balanced
Why? What happens to the boat's motion?
- Reasoning: The buoyant force of the water pushing the boat up is equal and opposite to the force of gravity pulling the boat down. Since the water is still, there are no significant unbalanced forces acting horizontally.
- Motion: The boat remains still (or moves at a constant velocity if it had been set in motion and all horizontal forces were balanced).
Scenario 4: A person pulling a heavy sled up a snowy hill.
Balanced or Unbalanced? Unbalanced
Why? What happens to the sled's motion?
- Reasoning: The person's pulling force is greater than the combined forces of friction and the component of gravity pulling the sled down the slope. This results in a net force uphill.
- Motion: The sled accelerates uphill (starts moving or speeds up).
Scenario 5: Two people arm wrestling, but neither person's arm is moving.
Balanced or Unbalanced? Balanced
Why? What happens to their arms' motion?
- Reasoning: Both people are exerting equal forces in opposite directions. The forces they apply are balanced, resulting in no net force causing motion in either direction.
- Motion: Their arms remain still.
Answer Key
Answer Key: Cool Down: Balanced or Not?
Scenario:
A skydiver jumps out of a plane. For a few moments, they speed up as they fall. Then, they open their parachute, and their speed quickly decreases until they are floating gently towards the ground at a steady pace.
-
During the first few moments, when the skydiver is speeding up, are the forces acting on them balanced or unbalanced?
Unbalanced -
Explain your reasoning:
Reasoning: When the skydiver is speeding up, the force of gravity pulling them down is greater than the air resistance pushing up. This difference in force causes a net downward force, making the skydiver accelerate (speed up). -
After the parachute opens and the skydiver is floating gently at a steady pace, are the forces acting on them balanced or unbalanced?
Balanced -
Explain your reasoning:
Reasoning: Once the skydiver reaches a steady pace with the parachute open, the increased air resistance pushing up is now equal to the force of gravity pulling them down. With balanced forces, there is no net force, so the skydiver moves at a constant velocity (a steady pace).