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 1 st 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 1 st Law of Motion
 Newton’s 1 st 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 1 st 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 1 st Law is also called the “Law of Inertia”

Newton’s 1 st 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/s 2 (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/s 2 in the formula W=mg
 W=weight (Newton, N)
 M=Mass (Kilogram, kg)
 G=Gravity (Same as acceleration, m/s 2 )

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