PRELAB QUESTIONS: (to be turned in upon arriving at lab) A spring initially has

Question

PRELAB QUESTIONS: (to be turned in upon arriving at lab)



A spring initially has no mass attached (far left in the figure above). When a mass (m1) is attached, the spring is stretched (middle in the figure above) and the mass hangs motionless from the spring.


3. Now imagine moving the mass on a string a few degrees to one side and holding it still with your hand. What forces are acting on the mass now? Which direction (if any) is the net force?


4. Now imagine letting go. In the instant after you let go, what forces are acting on the mass? Which direction (if any) is the total force?



5. Our second experiment involves timing how long it takes a ball to fall from a certain height. Given the time t it takes a ball to fall a distance y, starting from rest and experiencing only the force of gravity, how can you calculate g, the acceleration due to gravity?

Explanation / Answer

If something is not moving, then it's not accelerating so there's no net force on it. Either there is no force at all (unlikely, anywhere in the vicinity of a planet or star), or the forces balance out.

For the string and the spring, there is a force on the mass due to gravity pulling it down, and a force due to the string or spring pulling it up.

Forces are vectors; the size and direction both matter.

(4) there's a force directed up the string (strings are flexible, so that's the only way possible), and gravity down towards the ground. Since these two vectors don't line up, they don't cancel, and there's a net force on the mass causing it to move in a circle (at that instant, a force in a straight line tangential to the circle causing it to accelerate forward)

(5) s=1/2 * a*t^2 ,

where "a" is acceleration = g here,

s is distance and

t is time.

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