Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Friction is a force that exists when two surfaces rub up against each other. For example, this cup on ...

Julia Kagan is a financial/consumer journalist and former senior editor, personal finance, of Investopedia. Khadija Khartit is a strategy, investment, and funding expert, and an educator of fintech ...