Mass and Weight PDF

**MASS AND WEIGHT** Mass is defined as: - A measure of the quantity of matter in an object at rest relative to the observer.. - Consequently, mass is the property of an object that resists change in motion - The greater the mass of an object, the more difficult it is to speed i...

**MASS AND WEIGHT** Mass is defined as: - A measure of the quantity of matter in an object at rest relative to the observer.. - Consequently, mass is the property of an object that resists change in motion - The greater the mass of an object, the more difficult it is to speed it up, slow it down, or change its direction - Mass is a scalar quantity that has magnitude but no direction - Mass is measured in kilograms (kg) Sometimes mass may be given in grams (g) but this will need to be converted to kilograms when used in calculations **1000 g = 1 kg** **1 g = 0.001 kg** - **To convert g to kg, divide the mass in g by 1000** - **To convert kg to g, multiply the mass in g by 1000** **Weight** Weight is a gravitational force on an object with mass. - Since weight is a force, it is a vector quantity with both magnitude and direction - Weight is measured in newtons (N) **Worked example** i. An object has a mass of 4.5 kg. ii. State the mass of the object in grams (g). **Answer:** Step 1: State the conversion between g and kg 1 kg = 1000 g Step 2: Convert kg into g by multiplying m = 4.5 x 1000 [m = 4500 g] **Weight and gravitational field strength** - Weight is the effect of a** gravitational field** on a mass - Weight is defined as: **The force acting on an object with mass when placed in a gravitational field** - Planets have strong gravitational fields - Hence, they attract nearby masses with a strong gravitational force - Because of weight: - Objects stay firmly on the ground - Objects will always fall to the ground - Satellites are kept in orbit 5-1-4-weight-force Defining gravitational field strength - **Gravitational field strength **is defined as: **The force per unit mass acting on an object in a gravitational field** g = F/m - On Earth, this is equal to **9.8 N/kg** - Where: - g = gravitational field strength, measured in newtons per kilogram (N/kg) - F = force of weight, measured in newtons (N) - m = mass of object, measured in kilograms (kg) - An object in free fall in a vacuum, in a uniform gravitational field, will **accelerate **at a rate also known as  - Where g = acceleration of free fall - In this context, g = 9.8 m/s^2^ - Gravitational field strength and acceleration of free fall are **equivalent **quantities  **Mass vs. weight** - An object's mass **always **remains the same, regardless of its location in the Universe - The weight force exerted on the object will differ depending on the strength of the gravitational field in its location - For example, the gravitational field strength on the Moon is **1.63 N/kg**, meaning an object's weight will be about **6 times** less than on Earth  ***On the Moon, a person\'s mass will stay the same but their weight will be much lower*** - You can find more information about the gravitational field strength on different planets in the revision note [Gravitational field strength](https://www.savemyexams.com/igcse/physics/cie/23/revision-notes/6-space-physics/6-1-earth--the-solar-system/6-1-5-gravitational-field-strength/) **Worked example** NASA\'s Artemis mission aims to send the first woman astronaut to the Moon. Isabelle hopes to one day become an astronaut. She has a mass of 42 kg. Compare the difference between Isabelle\'s weight on Earth, and her weight on the Moon. Take the Earth\'s gravitational field strength as 9.8 N/kg, and the Moon\'s gravitational field strength as 1.6 N/kg.   **Answer:** **Step 1: List the known values** - Mass,  - Gravitational field strength on Earth,  - Gravitational field strength on Moon,  **Step 2: State the equation linking weight, mass and gravitational field strength** **Step 3: Rearrange to make weight the subject** **Step 3: Calculate the weight force exerted on Earth** **Step 4: Calculate the weight force exerted on the Moon** **Step 5: Compare the two values of weight** - The weight force is **greater** on Earth than on the Moon - This is because the Earth has a **larger** gravitational field strength than the Moon, so Isabelle\'s weight force is larger on Earth than on the Moon **Exam Tip** You won\'t be expected the learn the **exact **value of *g* (9.81 N/kg), but you will be expected to remember that ***g* = 9.8 N/kg** and use it in calculations **Using a balance** - The **weight **of two objects can be compared using a **balance** - Because the gravitational field strength is **constant **everywhere on Earth, this also allows us to measure the **mass **of an object   Types of balance, IGCSE & GCSE Physics revision notes ***A balance can be used to compare two different weights*** - **Balances **can be digital or analogue - The object being measured is placed on the balance - The reading given is **mass** in kg or g - **Force meters** or **newtonmeters **consist of a spring and hook - The object being measured is hung from the hook - The reading given is **weight **in N