Friday, April 5, 2013

Forces & Motion - An Explanation

Motion is all around us. We don't really notice it unless we stop and think about it. And Newton's 3 Laws of Motion control so much of our lives!

Our students have studied Motion in previous grades and we wanted to ramp up our Forces and Motion unit this year. To introduce the unit, we went on a Motion Hunt around our school. We made a T-Chart of things we use push and pull to move. Obviously, 3rd graders know what push and pull are and we want to challenge them in their understanding of science.

Next, we discussed Isaac Newton's 3 Laws of Motion. I used George Power's FREEBIE TpT ppt to help explain the Laws. We went through example of each Law.
First Law of Motion: An object at rest will stay a rest and an object in motion will stay in motion unless acted on by an outside force. This is sometimes called The Seatbelt Law. When you are in a car, moving at 35 mph, your body is also moving at 35 mph. If the car comes to a sudden stop, your body wants to stay in motion and will continue moving forward. The outside force (the seatbelt) stops your body and saves you from being hurt. Another example is a soccer ball kicked at recess, it will continue moving at a constant velocity (speed) until acted on/slowed down and stopped by the ground or grass (friction).

Second Law of Motion: Mass x Acceleration = Force  Basically, it takes more speed to move objects with more mass and less speed to move objects with less mass. For example, if you throw a bowling ball and a basketball (roughly the same size), the basketball will go farther because there is less mass weighing it down.

Third Law of Motion: For every action, there is an equal and opposite reaction. When I sit in a chair, my force is pushing down on the seat (action) and the seat is pushing up on me (opposite action). For me to rest on the chair, those forces must be equal. If my force was greater than the chair's, it would break and I would fall. If the chair's force was greater than mine, I would float off the chair. One of my students asked about a beanbag chair, and I thought that was a great example of a chair with less force (since you sink into the chair as you sit).

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