Final answer:
Investment is the most volatile component of GDP in the U.S., displaying rapid changes and causing significant fluctuations.
Step-by-step explanation:
The most volatile spending component of GDP in the United States tends to be investment rather than consumption by households. While consumption expenditure by households is the largest component of GDP, accounting for about two-thirds, it remains relatively stable over time. Investment, on the other hand, is subject to rapid changes due to its sensitivity to interest rates and economic expectations. Therefore, investment in things like businesses, new housing, and inventories typically shows more volatility and can lead to significant fluctuations within the GDP.