The product of force and time is?

1. Analyze the question

The question asks for the physical quantity defined by the product of force ($F$) and the time interval ($t$) over which that force acts.

2. Explain the concept

In Physics, particularly in the study of Newton's Laws of Motion, we look at how forces change the state of an object.

• Impulse is defined as the product of the average force applied to an object and the time interval during which the force acts. Mathematically, it is expressed as: $$Impulse (J) = Force (F) \times Time (t)$$
• Momentum is the product of mass and velocity ($p = mv$). According to the Impulse-Momentum Theorem, an impulse applied to an object is equal to the change in its momentum ($\Delta p$). While they are related, they are not the same thing.
• Inertia is the property of matter by which it continues in its existing state of rest or uniform motion in a straight line unless changed by an external force.
• Friction is a resistive force that opposes motion between two surfaces in contact.

3. Show the solution

• Step 1: Identify the formula for the given parameters. The formula for Impulse is $J = F \times \Delta t$.
• Step 2: Compare this with the options provided. The question asks for the product of force and time, which matches the definition of Impulse.
• Step 3: Verify against the other options. Momentum is $mv$, Inertia is a property (not a product of force and time), and Friction is a type of force. Therefore, Impulse is the only correct physical quantity.

4. Identify the answer

The correct option is A.

5. Exam Tip

To remember this easily, think of a football player kicking a ball. The "kick" is the Force, and the short duration the boot stays in contact with the ball is the Time. The result of that interaction is an Impulse, which causes the ball to gain Momentum (speed). Remember: Impulse = Force × Time.