Mass vs. Weight Mass – The quantity of matter in an object. It is also a measure of the inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, or change its state of motion in any way (kg).

Mass vs. Weight Weight –The force upon an object due to gravity. (N) Newton is the force applied to move a one-kilogram mass at an acceleration of 1m/s/s. Mass and weight are directly proportional to each other. The fact that mass and weight are directly proportional to each other means that we often confuse mass and weight in our daily lives. For example. As the mass (volume of matter) of an object increased, its weight also increases. If I compare the force exerted due to gravity on me vs. force due to gravity acting upon the book, the force due to gravity that I exerted is greater than that of the book. We saw this in lab. Generally as the mass of an object increased, the weight of the object also increased.

Mass vs. Weight Pound is a unit of weight in the USCS. 1 pound = 4.448 Newtons 130 pounds = 578.24 Newtons Due to confusion, there are now two different abbreviations for the pound: pound-mass (lbm) pound-force (lbf) 663 N = 150 lbf I don’t know about you. But when I tell my friend my weight. I don’t mean the force of gravity acting upon me. I simply mean how much matter is contained within my body. Because we are so close to the US we refer to our body weight in POUNDS! (USCS unit). Everywhere else in the world you would refer to your weight in kilograms. For example, when I lived in Europe it took me awhile to get use to the fact that my bags were weighted in kilos and without a conversion factor and calculator handy I was often guessing if my bags would be overweight when I flew home or not. Traditionally, the pound is a unit of weight (force exerted due to gravity) and is equal to 4.448 newtons. This is also what your textbook indicates. Therefore, if I express my weight of 130 pounds in Newton’s I would weight 578.24 N. Unfortunately, there is a great deal of confusion about the definition of the pound. Many physics authors using the unit to describe mass (volume); whereas others are using it to describe weight They now are abbreviating it to read pound-mass (lbm) and pound-force (lbf). This confusion is part of the reason that the use is starting to switch over to the IS, where the base unit of mass if the kilogram and the unit of force is the Newton. 663 N = 150 lbf

Mass vs. Weight Mass does not change with gravitational force. Inertia also does not change with gravitation force. (ex. shaking an object in space is just as difficult as it would be to shake it on Earth) 1 kg = 10 N 150 lbm or 66.3 kg Mass does not change with gravitational force. Imagine trying to weight something on a space ship in outer space, where this is no influnce exherted due to gravity. You would not even be able to keep the object on the scale, much less read it’s weight, because there would be no influence due to gravity. Its mass however, does not change. The volume of matter would be the same. If we took our man and shot him into outer space. The volume of matter he contains would not change.

Newton’s Second Law of Motion Newton’s Second Law of Motion states: “The acceleration of an object is directly proportional the net force acting on the object, is in the direction of the net force and is inversely proportional to the mass of the object.” We are going to break Newton’s Second Law of Motion into three parts and consider each part separately, so that we can put it all together and better under the law before us.

Newton’s Second Law of Motion Acceleration: is caused by force depends on the net force Acceleration is directly proportional to the net force: acceleration ~ net force 2x acceleration = 2x net force Whatever happens to acceleration will happen in equal quantity to the net force and vice versa. Acceleration is caused by a force. Example kicking a ball. You are exherting a force on the ball and the ball is accelerating because of the force you exerted. It also depends on a net force. If all forces were equal the ball would either remain stationary or continue to move in the same direction at the same speed. The acceleration of an object with double when the net forces on the object double. Three times the net force produces three times the acceleration. Therefore acceleration is directly proportional to the net force!

Newton’s Second Law of Motion Acceleration is also inversely proportional to mass. As mass increases, acceleration with a constant force will decrease. As mass decreases, acceleration with a constant force will increase. Acceleration ~ 1 . mass Acceleration is also inversely proportional to mass. We see this in our daily lives if we spend a lot of time with kids. We can push one child in the toy car at a certain acceleration, if we don’t change the amount of force we exert and push another child in the car, the acceleration of the car will be less. THE RATE OF CHANGE OF THE SPEED OF THE CAR WILL BE LESS! Inversely means that the TWO VALUES CHANGE IN THE OPPOSITE DIRECTIONS!

Newton’s Second Law of Motion Acceleration ~ 1 . mass Acceleration ~ net force Put it all together… Acceleration ~ net force As the net force increased the acceleration would increase by the same amount. Remember: 2X net force = 2X acceleration Therefore we now have

Newton’s Second Law of Motion Acceleration of an object is always in the direction of the net force! Acceleration ~ net force mass “The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.” Therefore we now have created Newton’s second law of Motion for ourselves!

Newton’s Second Law of Motion Acceleration ~ net force mass A ~ Fnet m If the ‘Fnet’ increases, ‘a’ will increase by the same amount If ‘m’ decreases, ‘Fnet’ will increase by the same amount We can express the law mathematically by the following equation: -