May the Force Be Qith You! May the Force Be With You!

What is a force? Force: Force: - a push or a pull that acts on an object - can change the motion of an object (move or stop it) - can change the shape of an object What different types of forces can you think of?

Forces can be categorized: a) Contact Forces: affect things they touch –Tension – force in a wire or rope –Friction – slows down motion –Elastic – spring-like object restores itself to its normal shape b) Action at A distance Forces: affect things without touching them –Gravitation – attraction between objects with mass –Electrostatic – force between charged objects –Magnetic – acts on certain metals

MASS vs WEIGHT MASS: MASS: –the amount of matter in a substance –is measured in kilograms (kg) 1000 grams (g) = 1 kilogram (kg) –best measured using a balance scale –is the same regardless of gravity (gravity pulls equally on objects of equal mass)

MASS vs WEIGHT WEIGHT: WEIGHT: –It is the FORCE on an object due to gravity! –Weight = mass x gravity –Measured in Newtons (N) – –NOTE: Bathroom scales actually measure “weight” (force), and not “mass”, even though the units used are in kilograms or pounds.

Different amounts of FORCE

Would you have the same WEIGHT on the Earth as on another planet? W= m x g Gravity on Earth = 9.81 N/kg Gravity on Earth = 9.81 N/kg My mass= 80kg My mass= 80kg W= m x g W= m x g = 80 kg x 9.81 N/kg = 80 kg x 9.81 N/kg =784.8 N =784.8 N Gravity on the Moon= 1.6 N/kg  less weight Gravity on the Moon= 1.6 N/kg  less weight Gravity on Jupiter = 27 N/kg  more weight Gravity on Jupiter = 27 N/kg  more weight

Weight = mass x gravity therefore increasing the GRAVITY causes an increase in weight (and vice versa) therefore increasing the GRAVITY causes an increase in weight (and vice versa)  DIRECT RELATIONSHIP The force of WEIGHT is directly related to both mass and gravity!! The force of WEIGHT is directly related to both mass and gravity!!

Measuring Force Force meters usually include a spring or elastic device that stretches or compresses Force meters usually include a spring or elastic device that stretches or compresses ex. newton gauges or spring scales 1 kg of mass would have a 1 kg of mass would have a weight (force of gravity) of 9.8 N on Earth W = m x g = 1kg x 9.8 N/kg = 1kg x 9.8 N/kg = 9.8 N = 9.8 N

Rapid Review: What forces are in action? Are they direct contact or action at a distance?

Your mass is 60kg. What is your weight on Earth? W = m x g = 60kg x 9.8N/kg = 60kg x 9.8N/kg = 588 N = 588 N What is your weight on a planet with gravity twice as strong as Earth? W = 60kg x 19.6N/kg What is your weight on a planet where the gravitational pull is one third as strong as Earth?