Museums collect and care for objects of scientific, artistic, or historical importance and make them available for public viewing through exhibits that may be permanent or temporary. Large museums are located in major cities throughout the world and more local ones exist in small cities. Most museums offer programs and activities for a range of audiences, including adults, children, and families, as well as those for more specific professions. Programs for the public may consist of lectures or tutorials by the museum faculty or field experts, films, musical or dance performances, and technology demonstrations. Many times, museums concentrate on the host region's culture. Although most museums do not allow physical contact with the associated artifacts, some are interactive and encourage a more hands-on approach. Modern trends in museum logy have broadened the range of subject matter and introduced many interactive exhibits, which give the public the opportunity to make choices and engage in activities that may vary the experience from person to person. With the advent of the internet, there are growing numbers of virtual exhibits, i.e. web versions of exhibits showing images and playing recorded sound. Museums are usually open to the public and sometimes charging an admission fee. Some museums have free entrance, either permanently or on special days, e.g. once per week or year. Museums are not open for the sole purpose of making a profit, unlike galleries that engage in the sale of objects. There are governmental museums, non-governmental or non-profit museums, and privately owned or family museums.