When your vehicle reaches a certain mileage (50,000 or more), you may notice more bouncing when driving. Your vehicle probably needs new struts and/or shocks. You will feel less control and more play when driving and possibly start to see more tire
A Shock is an absorber inside the spring that uses hydraulics to help decrease the vehicle from bouncing.
A Strut is more complex. Struts are the vehicle's "absorption factor". They support your vehicle's suspension. This means that Struts support your car's weight, your car's steering and help you drive properly.