A ballpoint pen and a rollerball pen differ primarily in their ink composition and writing experience. Ballpoint pens use a thick, oil-based ink that is less prone to smudging and dries quickly. This ink is dispensed through a small rotating ball at the pen's tip, which rolls across the paper to transfer the ink. The oil-based ink is more viscous, requiring more pressure to write, which can lead to a firmer grip and potentially more hand fatigue over extended use. Ballpoint pens are known for their reliability, longevity, and ability to write on various surfaces, making them ideal for everyday use and for those who need a pen that can withstand different conditions. Rollerball pens, on the other hand, use a water-based or gel-based ink, which is thinner and flows more freely than the oil-based ink of ballpoint pens. This results in a smoother writing experience with less pressure needed, which can be more comfortable for long writing sessions. The ink from rollerball pens tends to be more vibrant and can produce a more consistent line. However, it is more prone to smudging and may bleed through thinner paper. Rollerball pens are often preferred for their smoothness and the ease with which they glide across the page, offering a writing experience closer to that of a fountain pen. In summary, the main differences lie in the ink type and writing feel: ballpoint pens offer durability and quick-drying ink, while rollerball pens provide a smoother, more fluid writing experience with richer ink colors.

A ballpoint pen operates using a simple yet effective mechanism that involves a small rotating ball made of brass, steel, or tungsten carbide. This ball is seated in a socket at the pen's tip and is partially exposed. The pen's ink reservoir, which is a tube filled with viscous, oil-based ink, feeds ink to the ball through capillary action and gravity. When you write, the ball rotates as it moves across the paper. This rotation picks up ink from the reservoir and transfers it onto the writing surface. The ball acts as a continuous valve, controlling the flow of ink. Its rotation ensures that ink is evenly distributed, preventing blotting or smudging. The ink's viscosity is crucial; it must be thick enough to prevent leakage but fluid enough to flow smoothly. The ball's snug fit in the socket prevents ink from drying out and stops air from entering the ink reservoir, which could cause the ink to dry or clog. The pen's design ensures that the ball remains in constant contact with the ink and the writing surface, allowing for consistent ink flow. Ballpoint pens are favored for their reliability, durability, and ability to write on various surfaces. They are less prone to leaking compared to fountain pens and can write for extended periods without needing a refill. The design simplicity and efficiency of ballpoint pens have made them a ubiquitous writing tool worldwide.

Ballpoint pens can stop working for several reasons: 1. **Ink Depletion**: The most straightforward reason is that the ink has run out. Once the ink reservoir is empty, the pen will no longer write. 2. **Ink Drying**: If a pen is left uncapped, the ink at the tip can dry out, forming a blockage. This prevents the flow of ink from the reservoir to the paper. 3. **Clogged Ballpoint**: Dust, paper fibers, or dried ink can accumulate around the ball, obstructing its movement and preventing ink from flowing smoothly. 4. **Air Bubbles**: Air bubbles can form in the ink reservoir, disrupting the flow of ink to the tip. This can happen if the pen is dropped or stored improperly. 5. **Temperature Changes**: Extreme temperatures can affect ink viscosity. Cold temperatures can thicken the ink, making it difficult to flow, while high temperatures can cause the ink to become too thin or even evaporate. 6. **Ball Mechanism Failure**: The ball in the tip of the pen can become dislodged or worn out, preventing it from rolling properly and thus stopping the ink flow. 7. **Ink Quality**: Low-quality ink can lead to inconsistent flow or clogging. Some inks may also separate over time, affecting performance. 8. **Reservoir Damage**: Physical damage to the ink reservoir, such as cracks, can lead to ink leakage or drying out. 9. **Improper Storage**: Storing pens tip-up can cause the ink to flow away from the tip, leading to drying or air bubble formation. 10. **Manufacturing Defects**: Occasionally, a pen may have defects from the manufacturing process that affect its functionality. These factors can individually or collectively cause a ballpoint pen to stop working.

1. **Check the Ink Level**: Ensure the pen still has ink. If it's empty, replace it. 2. **Shake the Pen**: Hold the pen firmly and shake it to move the ink towards the tip. 3. **Warm the Pen**: Gently heat the tip with a hairdryer or by rubbing it between your hands to loosen any dried ink. 4. **Scribble on Paper**: Press the pen firmly on a piece of paper and scribble in circles or back-and-forth motions to get the ink flowing. 5. **Tap the Pen**: Lightly tap the pen on a hard surface with the tip facing down to dislodge any blockages. 6. **Use Rubbing Alcohol**: Dip the tip in rubbing alcohol for a few seconds to dissolve dried ink, then try writing again. 7. **Blow Air Through the Cartridge**: Remove the ink cartridge and blow air through the back end to push ink towards the tip. 8. **Clean the Tip**: Wipe the tip with a damp cloth to remove any dried ink or debris. 9. **Replace the Refill**: If none of the above methods work, consider replacing the ink cartridge or refill.

Some of the best brands of ballpoint pens include: 1. **Parker**: Known for its classic design and smooth writing experience, Parker pens are a staple in the world of ballpoint pens. They offer a range of styles from the affordable Jotter to the luxurious Parker Sonnet. 2. **Cross**: Cross pens are synonymous with quality and elegance. The brand offers a variety of ballpoint pens that are both stylish and reliable, such as the Cross Classic Century and Cross Edge. 3. **Montblanc**: A symbol of luxury, Montblanc pens are crafted with precision and high-quality materials. The Montblanc Meisterstück is particularly renowned for its timeless design and superior performance. 4. **Pilot**: Known for innovation and affordability, Pilot offers a wide range of ballpoint pens. The Pilot G2 is a popular choice for its smooth ink flow and comfortable grip. 5. **Uni-ball**: Uni-ball pens are appreciated for their consistent ink flow and durability. The Uni-ball Jetstream is a favorite for its quick-drying ink and smooth writing experience. 6. **BIC**: A household name, BIC pens are known for their reliability and affordability. The BIC Cristal is a classic choice for everyday use. 7. **Lamy**: German-engineered Lamy pens are celebrated for their modern design and functionality. The Lamy 2000 is a standout model, offering a sleek design and smooth writing. 8. **Fisher Space Pen**: Famous for its ability to write in extreme conditions, including zero gravity, the Fisher Space Pen is a unique and durable option. 9. **Zebra**: Zebra pens are known for their precision and comfort. The Zebra F-701 is a popular model, offering a stainless steel body and smooth writing. 10. **Paper Mate**: Known for their affordability and reliability, Paper Mate pens like the InkJoy series offer vibrant colors and a smooth writing experience.