P5

Describe the moment of a force as a measure of its turning effect, and give everyday examples.

A person pushing a swing will make the swing rotate about its pivot. A worker applies a force to a spanner to rotate a nut. A person removes a bottle's cork by pushing down the bottle opener's lever. A force is applied to a door knob and the door swings open about its hinge.

State Hooke's Law and recall and use the expression F = k x, where k is the spring constant.

force = constant x extension (F=kx): Hooke's Law states that within the elastic limit, the extension (x) of an object is directly proportional to the force (f) that causes the extension. When written mathematically, it is F ∝ x. That means, for any value of x, if you multiply it by a certain number, you'll get F.

Demonstrate understanding that weights (and hence masses) may be compared using a balance.

A true balance measures mass directly by comparing the unknown mass to a known mass, a process that is not affected by changes in gravity. A balance of this sort will give the same reading irrespective of location because gravity will act on both sides of the balance equally. Weighing balances measure mass, which is the amount of matter in something. A weighing balance measures mass directly by comparing the unknown mass to a known mass, which is not affected by changes in gravity. Therefore, a balance should give the same reading regardless of its location.

Know that the Earth is a source of a gravitational field.

Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body. The Earth's gravitational field (see gravitation) is manifested as the attractive force acting on a free body at rest, causing it to accelerate in the general direction of the centre of the planet. Every object with a mass has a gravitational field that pulls other masses closer to it however unless it has an extraordinarily large mass this is normally negligible but the earth does have an extraordinarily large mass and it's gravitational force is what keeps us on it. the earth is the source for the gravitational field around it.

Recognise that g is the gravitational force on unit mass and is measured in N/kg.

Gravitational field strength (g) is measured in newtons per kilogram (N/kg). The Earth's gravitational field strength is 9.8 N/kg. This means that for each kg of mass, an object will experience 9.8 N of force. Where there is a weaker gravitational field, the weight of an object is smaller.

Recognise that, when there is no resultant force and no resultant turning effect, a system is in equilibrium.

If there is no resultant force then a system is said to be in equilibrium . If the resultant force is not zero, a moving object will speed up or slow down - depending on the direction of the resultant force: it will speed up if the resultant force is in the same direction as the object is moving.

Perform and describe an experiment to determine the position of the centre of mass of a plane lamina.

In mathematics, a planar lamina (or plane lamina) is a figure representing a thin, usually uniform, flat layer of the solid. It serves also as an idealized model of a planar cross section of a solid body in integration.

Describe the determination of the density of an irregularly shaped solid by the method of displacement and make the necessary calculations.

It's difficult to calculate the volume of an irregular solid, so we use a slightly different method - we use the displacement of water. There are two ways to do this - if your solid is small enough to not take up much space in a measuring cylinder, then you can use just the measuring cylinder. If not, then use a displacement beaker. Calculating volume with a measuring cylinder: First, fill a measuring cylinder with water to about half its volume and record the volume of the water in the cylinder. Then carefully drop the solid into the water, making sure not to splash the water. Record the new volume. The initial volume reading is the volume of the water, and the final volume reading is the volume of the water + solid, so the difference between the two volume readings is the volume of the solid. Calculating the volume with a displacement beaker: Fill the displacement beaker with water, filling it as much as you can without having any water displaced. Place a measuring cylinder at the spout of the beaker (like in the diagram). Carefully place the solid into the beaker, without splashing any water. The measuring cylinder should collect all the displaced water. Read off the value of the volume of displaced water in the measuring cylinder and record it. This is equal to the volume of the solid in the displacement beaker. Note that for both these methods, you cannot use water absorbent solids (e.g. dry dirt, a sponge) as they will absorb some water. This means that the volume of the displaced water will be less than the volume of the solid. Okay, so now you have the volume of the irregular solid. All that's left is finding its mass using an electric balance, and calculating its density using the formula d = m / V and the appropriate units.

Recognise the significance of the term limit of proportionality for an extension-load graph.

Limit of proportionality' is another phrase for 'elastic limit'. They mean the same thing. The point at which the graph goes from being a straight line to a curved line is the limit of proportionality.

Describe an experiment to determine the density of a liquid and of a regular shaped solid and make the necessary calculations.

Liquid: So we've already established that to calculate density, we need to know the mass and volume of the substance that we're calculating the density of. To calculate the mass of a liquid, first, weigh the container that is going to hold the liquid on an electric balance (I'd recommend using a measuring cylinder or a volumetric flask as a container). Record the mass shown. Then add the liquid to the container (fill it up to the mark if it's a volumetric flask), and measure and record the mass of the container + liquid. The mass of container + liquid minus the mass of the container will give you the mass of the liquid. Now you need the volume of the liquid. Simply read the volume from the graduations on the measuring cylinder, or, if it's a volumetric flask and you've filled it up to the mark, you already know its volume (i.e. if you filled a 250cm3 volumetric flask to the mark, then you've got 250cm3 liquid). Note that 1ml = 1cm3 and 1litre = 1dm3. Now calculate the density of the liquid using d = m / V and the appropriate units. So we've already established that to calculate density, we need to know the mass and volume of the substance that we're calculating the density of. To calculate the mass of a liquid, first, weigh the container that is going to hold the liquid on an electric balance (I'd recommend using a measuring cylinder or a volumetric flask as a container). Record the mass shown. Then add the liquid to the container (fill it up to the mark if it's a volumetric flask), and measure and record the mass of the container + liquid. The mass of container + liquid minus the mass of the container will give you the mass of the liquid. Now you need the volume of the liquid. Simply read the volume from the graduations on the measuring cylinder, or, if it's a volumetric flask and you've filled it up to the mark, you already know its volume (i.e. if you filled a 250cm3 volumetric flask to the mark, then you've got 250cm3 liquid). Note that 1ml = 1cm3 and 1litre = 1dm3. Now calculate the density of the liquid using d = m / V and the appropriate units. Determining the density of a regularly shaped solid: When I say 'regularly shaped' solids, I mean ones that you can calculate the volume of using math - like a cube or cuboid, a cylinder, a prism, a pyramid, a sphere, etc. I'm going to assume you know how to calculate the volumes of the shapes listed above, but if you don't, please drop a comment below, and I'll update the notes to include them! So the first step is calculating and recording the volume of the solid. Then find and record its mass by weighing it on an electric balance. Calculate its density using the formula d = m / V and the appropriate units.

Distinguish between mass and weight.

Mass: Mass is a measure of the amount of matter in an object. Mass is usually measured in grams (g) or kilograms (kg). Mass measures the quantity of matter regardless of both its location in the universe and the gravitational force applied to it. Mass is a measurement of the amount of matter in some object. It depends only on what type of atoms the object is made of, and how many atoms there are. Mass is traditionally measured in kilograms (kg) Weight: weight, gravitational force of attraction on an object, caused by the presence of a massive second object, such as the Earth or Moon. Weight (symbolized w ) is a quantity representing the force exerted on a particle or object by an acceleration field, particularly the gravitational field of the Earth at the surface. The force with which a body is attracted to Earth or another celestial body and which is equal to the product of the object's mass and the acceleration of gravity. A measure of the heaviness of an object.

Understand that a micrometer screw gauge is used to measure very small distances.

Micrometer screw gauge is defined as an instrument that is used for measuring the diameter of thin wires, the thickness of small sheets such as glass or plastics. The micrometer screw gauge is used to measure even smaller dimensions than the vernier callipers. The micrometer screw gauge also uses an auxiliary scale (measuring hundredths of a millimetre) which is marked on a rotary thimble. A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for accurate measurement of components in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers.

Relate qualitatively pressure to force and area, using appropriate examples.

That means, for a fixed area, if you apply a huge amount of force, you'll be applying a large pressure on that area. For that same area, if you apply a smaller force, the pressure will be smaller.

Moment:

The Moment of a force is a measure of its tendency to cause a body to rotate about a specific point or axis. This is different from the tendency for a body to move, or translate, in the direction of the force.

Apply the principle of moments to the balancing of weightless beam about a pivot.

The Principle of Moments states that when a body is balanced, the total clockwise moment about a point equals the total anticlockwise moment about the same point. Moment =force F x perpendicular distance from the pivot d.

Describe qualitatively the effect of the position of the centre of mass on the stability of simple objects.

The position of the centre of gravity of an object affects its stability. The lower the centre of gravity (G) is, the more stable the object. The higher it is the more likely the object is to topple over if it is pushed.

Describe, and use the concept of, weight as the effect of a gravitational field on a mass.

The weight of an object is defined as the force of gravity on the object and may be calculated as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton. unlike most people think weight is just a force. When gravity acts on a mass there is a weight. it is measured in newtons and is calculated using the formula w = mg where w is weight, m is mass and g is the forces acting on an object (most of the time we use gravity). weight is the effect of a gravitational field on a mass.

Describe how forces may change the size and shape of a body.

When an external force acts on a body, it may change the direction it moves in, its speed, or cause it to start moving from rest (like when you kick a ball). Sometimes, the force might cause a rearrangement of the molecules making up the body, causing it to change in size or shape (e.g., crushing a can, stretching a spring).