Sofia Martinez
Plastic is a versatile material used in a wide range of applications, from disposable items to durable goods. When working with plastics, it's often necessary to calculate the weight of a plastic object, which can be achieved by determining its volume and density. The volume of plastic can be measured by completely submerging the plastic object in water and calculating the difference between the initial and final water levels. This volume measurement, along with the known density of the plastic type, allows for the calculation of mass and, subsequently, weight. Understanding the weight of plastic objects is crucial for various applications, including manufacturing, packaging, and recycling.
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What You'll Learn
Calculating weight from volume
The weight of a plastic object can be determined without weighing it if its volume and density are known. Weight is often used interchangeably with mass in everyday language, but they are different. Mass is the amount of matter in an object and is the resistance of an object to acceleration. Mass is constant regardless of location. Weight, on the other hand, is the force on a mass under the influence of gravity.
To calculate the weight of a plastic object, follow these steps:
- Obtain a piece of the plastic and identify the type of plastic you are testing.
- Look up the mass density of the plastic. Density is the mass-to-volume ratio, a physical property of every material. For example, water at 4 °C has a density of 1 kg/l, meaning that one litre of water weighs one kilogram.
- Measure the volume of the sample. Fill a large graduated cylinder with water to the 500 ml level. Immerse the piece of plastic completely in the water. Note the new water level. The difference between the new and original water levels is the volume of the object.
- Calculate the mass using the density equation: Mass = Density x Volume. Record the mass in kilograms.
- Calculate the weight using the acceleration due to gravity: Weight (N) = Mass (kg) x Acceleration due to gravity (m/s^2). On Earth, the gravitational acceleration is 9.81 m/s^2.
It is important to note that in the metric system, density has units of kilograms per cubic meter (kg/m^3) or grams per cubic centimeter (g/cm^3). When converting between grams and volume, ensure that the units of volume are cm^3 (mL).
In the context of transport, the term "volumetric weight" is used to refer to a calculation that takes into account both the volume and stackability of goods being transported. The volumetric weight is calculated using the formula: Volumetric Weight (kg) = Length (m) x Width (m) x Conversion factor (MLD/kg). The volumetric weight is then compared with the actual weight, and the higher value is chosen as the chargeable weight.
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Volume cost of raw materials
The volume cost of a raw material is the purchase cost of a unit volume of the material. It is a key factor in determining the cost of plastic manufacturing, yet many manufacturers overlook its importance. The volume cost of a raw material factors in the material's density, which the price per pound or kilogram does not. This provides a better basis for comparing materials.
To calculate the volume cost, multiply the specific gravity by the cost per pound or kilogram. The specific gravity value is usually found on the technical data sheet. It is the ratio of the density of a material to the density of a reference material, typically water, which has a density of approximately 1.0 g/cm3. Therefore, specific gravity and density can be assumed to be equivalent for a given material.
The density of a material affects the number of parts or unit lengths that can be produced per pound or kilogram. For example, Material Z has a much more attractive pricing of 40 cents less per pound. However, its specific gravity has a greater influence, resulting in the highest overall manufacturing costs. Thus, relying on price per pound alone may lead to costly mistakes.
The volume cost is especially important when polymers are compounded with additives. The density of the final product can change significantly when mineral fillers are added to reduce costs. For instance, replacing 50% of PVC resin with CaCO3 powder can lead to a cost reduction of 25%.
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Density and weight
Density is defined as the mass per unit volume under normal pressure and temperature. The density of plastic is calculated by dividing the mass of the material by the volume and is usually expressed in grams per cubic centimetre (g/cm3). The bulk density of plastic materials is the weight of material per volume and can be expressed in gram per cubic centimetre (g/cc), gram per cubic metre (g/cm), pound per cubic foot (b/cu ft), or kilogram per litre (KG/L).
The density of plastic can be determined using the density-gradient technique, ASTM D1505, where a material is placed in a liquid column of variable density with standard floats, usually glass beads of known density. The density of the material is then calculated based on its relative position to the floats in the column and the densities of the glass beads. Another method for determining the density of solid plastics, ASTM D792-98, involves testing solid plastics in water.
The density of plastic can be reduced by foaming molding, which is considered the most effective way to decrease density. This method involves adding a light material to the plastic blend, reducing the density by up to 50%. Alternatively, low-density blends such as ABS (Acrylonitrile Butadiene Styrene)/PP & PE can be added to the plastic to reduce its density.
The weight of a plastic object can be determined using its volume and density, without the need for weighing. The weight of an object is calculated by multiplying its mass by the acceleration due to gravity. On the Earth's surface, the weight of an object is calculated by multiplying its mass by 9.81 (m/s2). For example, to calculate the weight of a piece of acrylic plastic with a density of 1.18 g/cm3 and a volume of 50 cm3, we first calculate its mass using the density equation: mass = density x volume = 1.18 g/cm3 x 50 cm3 = 59 g = 0.059 kg. Then, we multiply the mass by the acceleration due to gravity: weight = mass x acceleration due to gravity = 0.059 kg x 9.81 m/s2 = 0.58 N.
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Graduated cylinders for volume measurement
Graduated cylinders, also known as measuring or mixing cylinders, are essential tools in any laboratory setting for measuring the volume of liquids. They are also used to indirectly measure the volume of solids by measuring the displacement of a liquid. They are typically made of glass or durable plastic and are narrow and tall to increase the accuracy of volume measurement. They have a plastic or glass base and a spout for easy pouring of the measured liquid. Graduated cylinders are also available in a wide and low version, which has a ground glass joint instead of a spout, allowing the liquid to be removed using a cannula.
Graduated cylinders are marked with volume graduations along their length, which allow scientists, chemists, and students to measure liquids with precision. These markings are typically in milliliters (ml), ranging from 10 ml to 2,000 ml, with some sources stating a range of 10 ml to 1,000 ml. The accuracy of a graduated cylinder is higher than that of a beaker because the graduations make it easier to fill, pour, measure, and read the amount of liquid. To ensure accurate measurements, it is important to place the cylinder on a flat surface and view it at eye level. The measurement is taken at the bottom of the meniscus, which is the curve formed by the liquid's surface tension.
Graduated cylinders are indispensable in many lab settings and are widely used in laboratories, schools, and industrial environments. They are particularly useful when exact volumes are necessary for chemical reactions, solution preparations, and laboratory testing procedures. They are also used in titrations to add precise amounts of one solution to another, ensuring controlled reactions.
Overall, graduated cylinders are essential tools for precise volume measurement, offering accuracy, versatility, and ease of use in a variety of applications.
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Weight and mass differences
Weight and mass are often used interchangeably in everyday language, but they are different. Mass is the amount of matter in an object and is the resistance of an object to acceleration. It remains constant regardless of location; for example, an astronaut with a mass of 100 kg on Earth will have the same mass on the moon. On the other hand, weight is the force on a mass under the influence of gravity. Weight is given by the relationship: weight = mass x acceleration due to gravity. On Earth, the gravitational acceleration is 9.81 m/s^2, while on the moon, it is only one-sixth of that, at 1.64 m/s^2.
The weight of an object can be determined by knowing its volume and density. Density is the material's mass per unit volume, typically expressed in g/cm^3 or kg/m^3. To calculate the weight of a plastic object, one must first identify the type of plastic and look up its mass density. Then, the volume of the plastic sample is measured. By rearranging the density equation, one can calculate the mass of the plastic sample. Finally, the weight can be calculated by multiplying the mass by the acceleration due to gravity.
Different types of plastics have varying weights. For example, acrylic sheet, known for its resistance to abrasion and impact, weighs 1.19 grams per cubic centimeter. Polycarbonate, which has higher impact and heat resistance, weighs 1.2 grams per cubic centimeter, slightly more than acrylic. Acrylonitrile butadiene styrene (ABS), widely used in refrigeration and automotive industries for its durability, has a lower density than acrylic or polycarbonate, weighing 1.03 grams per cubic centimeter. Polyvinyl chloride (PVC) is one of the lightest plastics available, known for its smooth matte finish and ease of painting or lamination. Vivak, a form of polyethylene terephthalate (PETG), has a weight of 1.27 grams per cubic centimeter, similar to polycarbonate.
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Frequently asked questions
The volume of plastic is the amount of space it occupies. It is typically measured in cubic centimetres (cm^3) or millilitres (ml).
To calculate the volume of a plastic object, you need to measure the volume of water displacement when the object is submerged. First, fill a graduated cylinder with water to a certain level, note the volume, then submerge the plastic fully. The difference between the new and original water levels is the volume of the object.
The volume cost of a raw material is the purchase cost of a unit volume of the material. It is calculated by multiplying the specific gravity by the cost per pound or kilogram.
If you know the volume and density of a plastic object, you can calculate its weight. First, calculate the mass using the density equation: mass = density x volume. Then, calculate the weight using the relationship: weight = mass x acceleration due to gravity.
In 2018, the United States generated 35.7 million tons of plastic.
