Post on 07-Aug-2015
What is Gravity?
• Non Contact Force
• “Pulling” force between objects
• All objects have gravity: bigger objects have more gravity than small objects.
What is Weight?• Weight is the force on an object due to
gravity.• Force is measured in Newtons• Scientifically, weight is a force so is also
measured in NewtonsWe can work out weight on Earth by multiplying mass times roughly 10.e.g. A man has a mass of 100 kg. What is his weight on Earth?
What is Weight?• Weight is the force on an object due to
gravity.• Force is measured in Newtons• Scientifically, weight is a force so is also
measured in NewtonsWe can work out weight on Earth by multiplying mass times roughly 10.e.g. A man has a mass of 100 kg. What is his weight on Earth? 1000 N
What about the moon?• The Earth’s acceleration due to
gravity is 9.8m/s2 (which is why we used 10 in the previous equation)
• The Moon’s acceleration due to gravity is 1.6m/s2
e.g. A man has a mass of 100 kg. What is his weight on the moon? 160 N
FrictionA contact force that opposes motion.
Acts in the opposite direction to motion.
A moving skateboard encounters friction
A stationary skateboard does not have friction
What is Gravity?
• Non Contact Force
• “Pulling” force between objects
• All objects have gravity: bigger objects have more gravity than small objects.
Gravity VS Friction