SI Unit of Momentum: Definition, Formula & Student Examples
Momentum is a fundamental concept in Physics and is essential for understanding motion, collisions, and the effects of forces on objects. Momentum describes the quantity of motion that an object possesses due to its mass and how fast it is moving. It helps explain everyday phenomena such as why heavier vehicles are harder to stop or how sport balls carry force as they move.
Definition and Formula of Momentum
In Physics, momentum is defined as the product of an object's mass and its velocity. The formula for momentum is:
Here, p represents momentum, m is the mass of the object, and v is its velocity. Both mass and velocity are key factors — if either increases, so does the momentum.
SI Unit of Momentum: Stepwise Derivation
The SI (International System of Units) unit of momentum is derived from its formula p = m × v. The SI unit for mass is kilogram (kg), and the SI unit for velocity is meter per second (m/s). Multiplying these gives the SI unit of momentum:
Therefore, the SI unit of momentum is kg·m/s.
Key Example: Calculating Momentum
Suppose a moving object has a mass of 2 kg and a velocity of 3 m/s.
So the object's momentum is 6 kg·m/s. This unit expresses the amount of motion contained in the object.
Relationship Between Force and Momentum
When a force acts on an object for a period of time, it changes the object's momentum. This concept links to impulse in Physics, which equals the change in momentum over a time interval. Impulse (J) = Force (F) × time (t).
The unit for impulse is Newton-second (N·s), which is dimensionally equal to kg·m/s. Hence, both kg·m/s and N·s can represent momentum in SI.
Units of Momentum: Table Comparison
| System | Unit | Symbol | Equivalent in SI |
|---|---|---|---|
| SI | kilogram meter per second | kg·m/s | kg·m/s |
| Alternate (SI) | Newton second | N·s | 1 N·s = 1 kg·m/s |
| CGS | gram centimeter per second | g·cm/s | 1 kg·m/s = 100,000 g·cm/s |
Step-by-Step: Solving a Momentum Problem
- Identify the mass (m) and velocity (v) of the object.
- Write the formula: p = m × v.
- Substitute the known values.
- Multiply and include the correct SI unit (kg·m/s).
Another Example
A ball with mass 0.2 kg moves with a velocity of 5 m/s. Calculate its momentum.
Therefore, the momentum of the ball is 1 kg·m/s.
Key Points and Physical Meaning
- Momentum combines both mass and velocity, making it a vector quantity pointing in the direction of motion.
- If velocity is zero, then momentum is also zero, regardless of the mass.
- Greater mass or velocity means greater momentum.
- The SI unit kg·m/s is always used for momentum in calculations and Physics questions.
Key Formulas for Application
| Concept | Formula | SI Unit |
|---|---|---|
| Momentum | p = m × v | kg·m/s |
| Impulse | J = F × t = Δp | N·s or kg·m/s |
| Force (From Momentum) | F = Δp / t | N (Newton) |
Practice and Explore Further
- Test your understanding of unit of momentum problems.
- Study the impulse-momentum theorem for collisions and force calculations.
- Understand how mass and momentum are related.
- See detailed applications in conservation of linear momentum in closed systems.
Summary
Momentum is the product of mass and velocity, and its SI unit is kg·m/s. This concept is crucial for solving problems related to motion and collisions. A clear understanding of units, formulas, and practical calculations will aid in mastering Physics fundamentals and scoring well in competitive exams.
FAQs on What is the Unit of Momentum in Physics?
1. What is the SI unit of momentum?
The SI unit of momentum is kilogram meter per second (kg·m/s). Momentum can also be expressed as Newton second (N·s), where 1 N·s = 1 kg·m/s. This unit is derived from the product of mass (kilogram) and velocity (meter per second).
2. How is momentum calculated in Physics?
Momentum (p) is calculated by multiplying mass and velocity:
• Formula: p = m × v
• Where m = mass of object (in kg), v = velocity (in m/s)
• The result's unit is kg·m/s (in SI system)
3. Why is momentum important in Physics?
Momentum is a fundamental concept in Physics because it describes the quantity of motion of an object and is conserved in isolated systems.
Main uses:
• Solving collision and projectile motion problems
• Explaining the law of conservation of momentum
• Understanding the effects of forces in real-world interactions
• Essential for exam topics in JEE, NEET, and CBSE Syllabus
4. Is Newton second (N·s) the SI unit of momentum?
Yes, the Newton second (N·s) is accepted as the SI unit of momentum. 1 N·s is exactly equal to 1 kg·m/s. Both units are used interchangeably for linear momentum and impulse in Physics.
5. What is the difference between momentum and impulse?
Momentum is the product of mass and velocity (p = m × v), measuring the quantity of motion. Impulse is the change in momentum (J = F × t = Δp) resulting from a force acting over time. Key points:
• Both have the same SI unit (kg·m/s or N·s)
• Momentum is a state; impulse is an event (change)
6. What is the unit of momentum in the CGS system?
In the CGS system, momentum is measured in gram centimeter per second (g·cm/s).
For conversion: 1 kg·m/s = 100,000 g·cm/s. Understanding system differences helps in Physics numericals and conversions.
7. How are the units of impulse and momentum related?
Impulse and momentum have the same units in Physics:
• SI unit: kg·m/s or N·s
• Both represent quantity of motion or its change
• Impulse = Change in momentum (Δp)
8. What is the dimensional formula of momentum?
The dimensional formula of momentum is:
• [M1 L1 T-1]
Here, M = mass, L = length, T = time. This helps in unit analysis and dimensional checks for Physics problems.
9. What is the formula and unit for change in momentum during a collision?
The change in momentum (Δp) during a collision is given by:
• Δp = m × (vfinal - vinitial)
• Unit: kg·m/s or N·s
This is directly related to the concept of impulse where impulse = change in momentum.
10. How can you convert momentum units between SI and CGS systems?
To convert momentum from SI to CGS:
• 1 kg·m/s = 1000 g × 100 cm/s = 100,000 g·cm/s
• Conversion factor: 1 kg·m/s = 1 × 105 g·cm/s
This helps in solving cross-system numerical problems in Physics examinations.
11. In which common Physics problems is the unit of momentum most frequently used?
The unit of momentum is widely used in:
• Collision and explosion calculations
• Projectile motion analysis
• Impulse-momentum theorem problems
• Force and time relationship applications
This unit is crucial for exam topics related to Newton’s Laws of Motion.
