Barbells and dumbbells are the two main types of free weights. Using this type of resistance does not restrict your range of motion the way a weight machine does. With free weights, your movements more closely resemble real-life movements. Although you can do the same exercises with both, dumbbells and barbells each have their own advantages and drawbacks.
Barbells are long, straight metal bars with sleeves on the ends to hold weight plates. The two types of barbells are standard and Olympic. Olympic barbells are a little more than 1 inch thick in the middle with 2-inch, rotating sleeves. They are 7 feet long and weigh 45 lbs. The entire length of a standard barbell is 1 inch thick. They are between 5 and 6 feet long and weigh between 15 and 30 lbs. Most standard barbells can hold up to 200 lbs., but Olympic barbells can handle loads over 800 lbs.
Dumbbells are short barbells, 10 to 15 inches long. You hold a dumbbell in one hand. Adjustable dumbbells are short, straight bars with sleeves for weight plates. They are available with standard, 1-inch, or Olympic, 2-inch, sleeves. The length of the weight sleeves on an adjustable dumbbell limits how much weight you can load on the bar. Hex dumbbells are fixed-weight dumbbells that are available in 5-lb. increments, between 5 lbs. and 100 lbs.
Advantages of Dumbbells
Dumbbells offer an increased range of motion for some exercises. Consider a bench chest press. Using a barbell limits your range of motion to the vertical pressing movement, but with dumbbells you can also bring the weights together at the top of the movement, increasing the range of motion. Hex dumbbells are convenient if you change weight often since you don't have to slide weight plates on and off. Dumbbells allow you to work your body unilaterally, one side at a time. If your left bicep is weaker than your right, you can focus on just the left side with dumbbells.
Advantages of Barbells
Some exercises, although you can do them with dumbbells, are designed to be performed with a barbell. Competitive weightlifters, who compete on two exercises -- the snatch and the clean-and-jerk -- only use Olympic barbells. Barbells allow you to lift more weight. A barbell holds more weight than a dumbbell and is safer to use with heavy weights, since you control the bar with two hands, not just one.