Lesson Plan: Introduction to Forces

1 NSTA Conference, Portland ELLs in the Secondary Science Classroom November 21, 2008 UMBC STEP T for ELLs Program Lesson plan : Introduction to Forces Unit Forces and Motion Curriculum References Goal 3: The student will be able to demonstrate the ability to measure and describe characteristics of moving objects and their interactions within a system. The student will be able to (a) define force and (b) explain how Forces acting on an object cause a change in position. Objectives Students will be able to: Define force . Draw vector diagrams to indicate magnitude and direction of Forces acting on objects.

2 Teacher Materials Overhead projector, Transparencies, Transparency markers, Book cart, Balloon Rocket set-up Student Handouts: Exploring Forces , Notes - Balanced and Unbalanced Forces , Using Vectors to Represent Net force Student Materials Newton carts, pennies and rulers Reference Prentice Hall Science Explorer: Physical Science textbook Warm-up (5 Minutes) Collect homework: Student read pp. 312-317 and completed Section Review, p. 317, #1-4. Have students respond to the following. 1. When drawing vectors we use arrows to show _____ and _____.

3 (Answer: magnitude and direction) 2. How can you change an object s motion? (Students responses may vary.) Engagement (10 Minutes) Instruct students to take a look at the following demonstrations. Observe each interaction identify what causes objects to move in each situation. Demo 1: Push a motionless book cart. Students think, pair, share & record (TPS). Demo 2: Pull a motionless cart. TPS Demo 3: Drop a penny. TPS Demo 4: Ask two students to hold opposite ends of the string to which the balloon rocket is attached.

4 Blow air into the balloon and immediately pinch the open end to prevent air from escaping. Instruct students to observe what happens when I release the balloon. TPS Instruct students to consider the four demonstrations. Given what you observed, reconsider your response to the last warm-up question. How can we change an objects motion? Exploration (25 Minutes) Inform students that, changes in motion occur when a force (a push or a pull) are applied to objects. As with velocity, we can use vectors to make predictions and describe how Forces affect motion.

5 In the following exercise, we will take another look at the demonstrations that you just observed. This time you will draw diagrams in which you use vectors to show the size and direction of the Forces acting on the objects. Distribute EXPLORING Forces handout (see next page). Teacher will complete the first interaction and diagram with the students. Students will work in groups to perform remaining interactions and draw the corresponding vector diagrams. Assign each group a diagram that the group will be responsible for sharing with the class.

6 Allow groups to share and respond to other groups diagrams. Explanation (20 Minutes) Mini-lecture: Balanced and Unbalanced Forces Instruct students to take notes while you explain the key concepts with examples (see below). NSTA Conference, Portland ELLs in the Secondary Science Classroom November 21, 2008 UMBC STEP T for ELLs Program Key Concepts A force is a push or a pull Vectors show the magnitude and direction of Forces . The magnitude or strength of a force is measured in a unit called a Newton (N).

7 The total force on an object after all Forces are added is called the net force . Unbalanced Forces cause objects to start moving, stop moving or change directions. Balanced Forces acting on an object do not change an object s motion. Inertia is an object s tendency to resist changes in motion. Newton s 1st Law of Motion- an object at rest will remain at rest and a moving object will continue to move at constant velocity unless acted upon by an unbalanced force . Elaboration/Extension (10 Minutes) In the following exercise, students will read two scenarios, draw the corresponding vector diagrams and calculate net force .

8 Distribute USING VECTORS TO REPRESENT NET force (see below). Collect and evaluate students diagrams. Evaluation Closing Activity (10 Minutes) Exit Tickets: Using Vectors to Represent Net force Exit Ticket- Why do we use force vectors? EXPLORING Forces Directions - Complete each interaction and draw a diagram that includes the following: A sketch of the moving and/or motionless object upon which the interaction occur. Arrows that show the relative size and direction of the Forces applied to the object.

9 Be sure to label each arrow. In addition, record observations about the object s motion. You should refer to the example that you complete with the teacher. Interaction Vector Diagram Observations Gently push the Newton cart with your finger Two people attempt to pull the Newton cart in opposite directions. Each person uses an equal amount of force . Two people push the cart at the same time from opposite sides. One person applies a greater force than the other person. Hold a penny 20cm above the table, and then release the penny.

10 USING VECTORS TO REPRESENT NET force Directions The following scenarios describe an interaction. For each, draw a vector diagram that shows all of the Forces involved. Afterward, calculate the net force and make the corresponding vector. Scenario Vector Diagram Net force A car stops at stop sign. Suddenly a truck hits the car from behind applying a force of 50N. In a game of tug-of-war, one team pulls the rope to the right with a force of 20N. With a force of 15N the other team pulls the rope.