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Weight. Weight is a force!. Weight is the force of gravity that one body (typically, planet size) exerts on another. To calculate weight, we modify this equation on your formula chart: F = ma The weight equation is: W or F g = mg where g = 9.8 m/s 2 = gravitational accel .
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Weight is a force! • Weight is the force of gravity that one body (typically, planet size) exerts on another. • To calculate weight, we modify this equation on your formula chart: F = ma • The weight equation is: W or Fg = mg where g = 9.8 m/s2 = gravitational accel. • Note: The symbol W can also mean Work.
Weight and mass are not the same! • Mass is a measure of the amount of matter in an object. It also measures the object’s inertia, resistance to changes in motion. • Weight is a measure of how much force a planet exerts by gravity on an object. • Mass is measured in SI units of kg. Weight is measured in SI units of N (Newtons) like any force.
Weight & Mass calculations • How much is the weight of a 10 kg object on Earth? Answer: Fg = (10 kg)(9.8 m/s2) or 98 N (not pounds!) • How much mass does a 49 N rock have? Answer: m = Fg/g = 49 N /9.8 m/s2 or 5 kg • Weight (on Earth) will always be number about 10 times bigger than mass.
Weightlessness • Even in space your weight is not zero. It is less than it is on the Earth’s surface. • Weightlessness is the sensation of feeling zero weight when an object is in free fall. In space, you are in free fall toward some body, be it the Earth, Moon, Mars, Sun,… • Free fall is accelerated motion due only to gravity and no other force.
Weight & Normal Force • For objects sitting on a surface there is a force keeping the object from falling. That force of the surface pushing on the object perpendicular to the surface is called the normal or supportforce. • In many cases, Fn balances or equals Fg providing a condition of equilibrium in the vertical direction.