^{Physics 1:  Mass, Speed, Acceleration, Force, Weight}

Week 1:  mass, speed, acceleration, force, weight

mass:  the amount of matter (atoms) found in a solid, liquid, or gas

      example:  one atom has a small amount of mass, the Earth’s mass is large

   the metric unit of mass is the gram (often abbreviated g or gm) and its friends

      one gram of mass is found in one paperclip; there are 15 grams of fat in a cheeseburger

      1 kilogram = 1000 grams.  most people are 50-100 kilograms of mass

   the English unit of mass is the slug but no-one in the US uses slug.  see “weight” at bottom of page

speed:  how fast, the distance traveled in a certain amount of time

      example:  60 miles traveled in 1 hour = 60 miles per hour

   units of speed:  meters/second, kilometers/hour, miles/hour, feet/second, etc.

acceleration:  a change in speed or a change in direction of a moving object is acceleration

   change in speed:  a car accelerates from 20 miles/hour to 50 miles/hour over a 1 hour period

      how much change in speed in how much time? change in speed divided by change in time

      30 miles per hour change in 1 hour time = 30 mph per hour

   change in speed:  a bullet decelerates from 220 meters/second to 100 m/sec in 3 seconds

      (220 m/s – 100 m/s) / 3 seconds = (120 m/s) / 3 sec = 40 m/s per second = 40 m/s²

   units of acceleration: metric,  meters per second squared, m/s², etc.

   units of acceleration:  English, feet per second squared, miles per hour², etc.

Force:  force is mass times acceleration.  force is the push needed to accelerate a mass.

   need a force to change the speed of a moving mass.  need force to change direction of moving mass

      example:  the force that decelerates a 50 gram bullet 40 meters per second every second is:

         force =  50 grams X 40 m/s²  =  2000 grams x m/s² 

   units of force, metric:  grams x m/s²  or (g x m)/s² ; (kg x m)/s²  = 1 Newton

   unit of force, English:  the pound and the ton.  see section below on weight.

Weight:  a special kind of force, related to the attraction between a mass and the Earth

   masses that are dropped show an acceleration of about 10 m/s²  or 31 feet/s²

      this special acceleration is called “little g”, the “Earth’s gravitational acceleration”

         100 kilograms x  10 m/s²  = 1000 kg x m/s²  = 1000 Newtons of weight

         100 slugs x 31 feet/s² = 100 pounds of weight  (yes, the math is correct)

            [because “little g” is constant, we often use “weight” (100 pounds) instead of mass

 
return to top of page

return to science topics page

return to main course page

-30-