Newton

1
Newtons Cannon or Mountain

• Ch. 4 A projectiles path is parabolic as it
  goes up down. NEWTONS IDEA (in the 1600s!)
  Put a large cannon on a large mountain. Shoot
  cannon balls (projectiles) at faster faster
  velocities. Eventually, the initial velocity is
  fast enough that the Earth's curvature must be
  taken into account in looking at the path. If the
  initial velocity continues to increase, the path
  extends farther farther around the Earth.
  Finally, at some critical velocity (Newton
  estimated 40,000 km/h!) the path would go around
  the Earth all the way eventually past the
  starting point keep on going.
• It would keep on falling forever!
• ? The projectile would ORBIT the Earth! This is
  essentially what happens when a satellite is put
  into orbit.
• Ch. 4 A projectile is in free fall in Earth's
  gravity. When an object orbits the Earth, it also
  is in  free fall!  Maybe it will be easier now
  to understand why objects in orbit are in
  free fall?

2

• To keep an object in orbit, the
• Gravitational Force provides the Centripetal
  Force!
• F (mv2)/r G(mME)/r2
• Figure Newtons Cannon
• showing parabolic projectile
• paths becoming orbits as the
• initial velocity increases.
• Many web pages (11,000 hits on Google)
• are devoted to this. Some have animated
• illustrations, where the user can specify the
• initial velocity see the path (orbit) it will
  follow. Typical web pages
  http//www.waowen.screaming.net/revision/forcemot
  ion/ncananim.htm
• http//www.smaphysics.ca/phys40s/field40s/newtmt
  n.html
• http//www.astronautix.com/lvs/n
  ewannon.htm