Ballasts are weight put in F1 cars to ensure better balance and handling. Putting ballasts in F1 cars is part of tuning the vehicle. Teams now use lightweight materials for F1 cars and put these weights to get better weight distribution.
The shape of the ballast depends on the team’s needs and usually varies from team to team. It is usually placed on the front side of the vehicle as shown in the photo. Since teams use extremely light material for chassis, ballasts are used to meet the minimum weight limit.