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Science Starter!. John weighs 735 N on Earth. What is John’s mass in kilograms? What would John’s mass be on the moon where g = 1.6 m/s 2 ? What would John’s weight be on the moon where g = 1.6 m/s 2 ? . F g = 735 N F g = mg g = 9.8 m/s 2 735 = (m) (9.8 m/s 2 )
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Science Starter! John weighs 735 N on Earth. • What is John’s mass in kilograms? • What would John’s mass be on the moon where g = 1.6 m/s2? • What would John’s weight be on the moon where g = 1.6 m/s2?
Fg = 735 NFg = mg g = 9.8 m/s2735 = (m) (9.8 m/s2) m = ? m = 75 kg • m = 75 kg 3. m = 75 kg Fg = mg g = 1.6 m/s2Fg = (75) (1.6 m/s2) Fg = ? Fg = 120 N
The “Normal” Force Contact force between surfaces (support)
Scales Measure the Normal force …. Not WEIGHT! Normal force – “Apparent” weight “The scale reads 540 N” FN = 540 N Ex: – Scales on an incline – Scales on an accelerating surface (stepping on a scale in an elevator)
Example 1 Joey has a mass of 60 kg. He stands on a scale in an elevator. As the elevator begins to move upward, the scale reads 658 N. • Draw a free-body diagram of Joey. • Write an “FNet Equation” in the horizontal vertical directions. • Determine the acceleration of the elevator.
Example 2 Joey has a mass of 60 kg. He stands on a scale in an elevator. What would the scale read if the cable suddenly snapped and the elevator was in free-fall? • Draw a free-body diagram of Joey. • Write an “FNet Equation” in the horizontal vertical directions. • Determine the scale reading.
“Weightlessness” Weightlessness: Absence of a normal force (free-fall) FN = 0 N, but Fg and “g” still exist! Vomit Comet Space Station