Newton’s 1st Law of Motion

Motion and Forces All motion happens because there is a force. Newton’s Laws describe the relationship between motion and force.

Forces Forces are anything that make an object start moving or make an object slow down or stop. There are balanced and unbalanced forces. Unbalanced forces make an object start moving or they make an object speed up or slow down if it is already moving. Balanced forces mean that an object is at rest or that it has a constant speed.

Newton’s 1st Law of Motion If you slide your book across a carpeted floor, it will eventually stop. Any ideas why? What about if you slide a book across a surface like ice? FRICTION!!!!

Newton’s 1st Law of Motion Newton’s 1st Law of Motion states: “An object at rest will remain at rest and an object in motion will remain in motion unless acted on by an unbalanced force. Why do you think there are seatbelts in cars? http://teachertech.rice.edu/Participants/louviere/Newton/carandwall.gif

Newton’s 1st Law of Motion Inertia is the tendency of an object at rest to remain at rest or an object in motion to continue in motion. All objects resist changes in motion, so all objects have inertia. Newton’s 1st Law is also called the “Law of Inertia”

Newton’s 1st Law of Motion Mass is a measure of inertia. An object with a small mass has less inertia than an object with a large mass. Therefore, it is easier to move an object with a small mass. Ex. It is easy to hit a baseball with a bat and send it flying in the air, but it is hard to do the same with a bowling ball.

Mass vs. Weight All objects have mass. Mass is the amount of matter an object has. Weight is a measure of the gravitational force that is exerted on an object. Remember that on Earth gravity is different than in space or on other planets (related to Earth’s size) All objects feel a pull towards the center of the Earth which is why all objects fall downward at a rate of 9.8 m/s2 (constant rate that never changes!)

Mass vs. Weight Even though your weight might be different, your mass will still be the same (what you are made of does not change!) To calculate “true” weight, you must use the gravitational constant 9.8 m/s2 in the formula W=mg W=weight (Newton, N) M=Mass (Kilogram, kg) G=Gravity (Same as acceleration, m/s2 )

Newton’s 1st Law Video Clip http://www.youtube.com/watch?v=tbpqRSip4to http://www.youtube.com/watch?v=7702nTbov9c&feature=related

Mass vs. Weight Practice Note: 1kg. =2.2 lbs To calculate your “true” weight, you would divide your weight in pounds by 2.2kg. 150 lbs/2.2 kg/lbs=68.18 kg Suppose you wanted to convert your weight from kg to pounds. You would simply multiply your weight by 2.2 kg. 75kg x 2.2= 165 pounds