Above all, brake pads are mainly affected by heat and friction. To stop the car would require a calliper that has a strong enough device to clamp onto the brake disc or rotor. Friction causes wear on any surface because the two sides are rubbing against each other. Wearing out the surface of the brake pad could take away the compounds that assist with deceleration. Friction is used between the disc and the pad so when the calliper squeezes the two pads onto the disc, it will slow down the car.
The more you use the braking system, the hotter the pads will get as friction causes heat. The high temperature also decreases the performance because of a term called brake fade. The driver will also have to apply the pedal much sooner so that he brakes on time to avoid collision.
A common term for this in the vehicle industry is brake fade. This means that when the pads reach a high temperature, the binding agents or resins that are used to bind the compounds together convert to gas which could cause the pads to slide uncontrollably. This is usually something that happens once or twice and usually settles itself.
Did you know that brake fluid could also damage and affect the pads? If there is fluid on the pads it usually means that there is a leak which could compromise braking quality. The stickiness on the brake pad could also accumulate dirt and grim over time which will also affect the quality of your deceleration speed.
If you suspect that something is affecting the brake pads then you will notice different sounds. Sounds that you should listen out for include squeaking when applying the pedal, squealing and metallic grinding. These sounds could also be related to disc or rotor problems. Longer distances to stop could also be a cause of worn out pads.