(2007? Xiaoling usually writes with a ballpoint pen with a spring. She wants to estimate the elasticity of the small spring of the ballpoint pen.

Need a balance to measure the quality of ballpoint pen;

(2) (1) Place the ballpoint pen vertically on the desktop near the instrument scale;

(2) Press the ballpoint pen head tightly on the desktop and record the reading of the pen tip X1;

③ Suddenly loosen the ballpoint pen and observe and record the reading x2 when the pen tip reaches the highest point;

④ Measure the mass m of ballpoint pen with a balance;

(3) The increase of gravitational potential energy of ballpoint pen equals to the decrease of kinetic energy, and the decrease of kinetic energy equals to the decrease of elastic potential energy, so the increase of elastic potential energy is △ EP = mg (x2-x1);

So the answer is: (1) meter ruler, balance;

(2) (1) Place the ballpoint pen vertically on the desktop near the instrument scale;

(2) Press the ballpoint pen head tightly on the desktop and record the reading of the pen tip X1;

③ Suddenly loosen the ballpoint pen and observe and record the reading x2 when the pen tip reaches the highest point;

④ Measure the mass m of ballpoint pen with a balance;

(3)mg(x2-x 1)。