OKLAHOMA ACADEMIC STANDARD FOR SCIENCE: 3-PS2-1 MOTION AND STABILITY: FORCES AND INTERACTIONS 3RD GRADE OBJECTIVE: Students who demonstrate understanding can plan and conduct investigations on the effects of balanced and unbalanced forces on the motion of an object. CORE IDEAS: 1. Each force acts on one particular object and has both strength and a direction. 2. An object at rest typically has multiple forces acting on it, but they sum to zero net force on the object. 3. Forces that do not sum to zero can cause changes in the object’s speed or direction of motion. 4. Objects in contact exert forces on each other. ASSESSMENT BOUNDARY: • • • Assessment is limited to one variable at a time: number, size or direction of forces. Assessment does not include quantitative force size, only qualitative and relative. Assessment is limited to gravity being addressed as a force that pulls objects down. MATERIALS REQUIRED: • Gravitate Kit o o o 2 rubber hoses Braces Legs • Measuring Tape • Balls of varying sizes and weights • Scale (for weighing balls) • Stopwatch 3-PS2-1: Motion and Stability: Forces and Interactions PREPARATION: 1. 2. 3. 4. Set up the track. Measure and record the length Radius of the loop R._____m Measure and record the height H. _____m Measure and record the mass of the moving object. _____kg PROCEDURE: Core Idea #1: Each force acts on one particular object and has both strength and a direction. 1. Release the mass. If the top of the track is flat, you may need to give the object a gentle push. 2. Did the object make the full circle? Yes or No. a. If yes, then reduce the height. Do not change the radius of the circle. It is a control. Record the new H ____ m Try again until you find the minimum PE needed for the object to make a full circle. b. If no, then raise the height. Do not change the radius of the circle. It is a control. Record the new H ____ m Try again until you find the minimum PE needed for the object to make a full circle. Assess: Ask questions to help the students identify the correlation between the force of the push or the height of the track and the distance the object travels. Core Idea #2: An object at rest typically has multiple forces acting on it, but they sum to zero net force on the object. 1. Place the ball on the flat surface at the top of the track and observe that it is stationary. a. What force(s) acting on the ball cause it to remain stationary? Why? b. What force(s) acting on the ball might cause it to move? Why? 2. Test their theories. Assess: Ask questions to help the students identify various forces acting on the object. What forces impact the direction of the object? Core Idea #3: Forces that do not sum to zero can cause changes in the object’s speed or direction of motion. 1. Ask the students to identify forces that might make the ball travel faster, slower, farther, etc. 2. Test their theories. 3. Did the theory work? Is there another way to impact the object’s speed or direction? 4. What forces are at work to keep the ball on the track as it completes the loop? Assess: Ask questions to help the students identify the forces that affect the speed and distance of the ball. 2 3-PS2-1: Motion and Stability: Forces and Interactions Core Idea #4: Objects in contact exert forces on each other. 1. Place 1 ball on the flat surface at the beginning of the track. 2. Place a second ball on the low point of the track prior to the loop. a. What will happen when the first ball hits the second ball? b. What kind of energy transfer will occur? 3. Give the first ball a gentle push and observe the forces exerted. Assess: Ask questions to help the students identify the forces exerted when objects are in contact. 3

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