1. Universal Forces
12.4 Assessment Qs 1-4

2. 1. Which universal force can repel as well as attract?
Electromagnetic force is associated with charged particles.  
Electric force and magnetic force are the only forces that can both attract and repel.
Electric and magnetic force are two different aspects of the electromagnetic force.

3. 2. Which universal force acts to hold the nucleus together?
Two forces,
the strong nuclear force and
the weak nuclear force, act within the nucleus to hold it together.

4. 3. State in your own words what is meant by Newton’s law pf universal gravitation.
Newton's law of universal gravitation states that every object in the universe attracts every other object.

5. 4. How does friction with the atmosphere affect the speed of an artificial satellite?
Much like the moon, satellites in high orbits only need the centripetal force provided by gravity and its inertia to maintain its orbit.
Satellites in a low orbit, however, are slowed by friction with Earth's atmosphere.
As a satellite loses speed, it loses altitude.
Eventually the satellite reenters Earth's atmosphere and burns up.