Orbital motion -- Radial force
Newton’s laws imply forces in planetary orbits
- For a circular orbit, the velocity is continuously changing
- consider constant speed in a circle
- draw an arrow, representing the velocity
- length of arrow is speed,
- direction of arrow is direction of velocity
- arrow rotates around in space
- for small time intervals
- change of arrow (i.e. acceleration) perpendicular to arrow
- Newton proved this with Calculus
- Orbital force is in radial direction for circular motion
- Test with ball orbiting prof. on a string
- string only transmits tension force
- no compression or sideways forces
- tension force is radial, orbit is circular