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The aim is to move at a steady speed, not to go as fast as possible. Do not stand close to where people are running or cycling. Do not leave the school grounds unless you have permission to do so. In athletics contests, runners are usually timed from the moment when the race starts to when they cross the finishing line. Your task is to measure the speed of someone moving quickly in the school grounds. They may be running or cycling. You should try to develop a method that is as accurate as possible. How accurately can you measure the time taken? Compare your results and try to explain any differences. This may help you to refine your technique. How can you decide whose is best?

What is its speed? Show the correct units. How far will it travel in one day? Give your answer in km. After five minutes, it reached the highway, where it was able to speed up. After ten minutes, it was forced to stop because of congestion. B The graph becomes steeper. The distance of the coach from its starting point is increasing more rapidly.

It is moving faster. C The graph is flat horizontal. The distance of the coach from its starting point is not changing. It is stationary.

The slope of the distance—time graph tells us how fast the coach was moving. The steeper the graph, the faster it was moving the greater its speed. Calculating weight We have seen that an object of mass 1 kg has a weight of 10 N; an object of mass 2 kg has a weight of 20 N; and so on.

Activity 3. In science, we use instruments to make measurements. For example, we use a balance to measure the mass of an object. But some balances are more sensitive than others.

For example, if you weigh yourself, the scales may give your mass to the nearest g or 10 g. Digital kitchen scales may give the mass of flour to the nearest gram. A lab balance may measure to the nearest milligram or better.

In this activity, you will test your own sensitivity. How good are you at comparing the masses of two objects? There are two methods that you can use to compare the masses of two objects. Method A: Pick up an object in one hand. Give yourself enough time to assess its mass. Moving your hand up and down can help when assessing the mass of an object. Then put it down and pick up another object. Assess its mass. Which has the greater mass? Compare masses that are similar.

Which method is more sensitive? What is the smallest difference in mass that you can detect? For example, if you compare a g mass with a g mass, can you tell the difference? Questions 3. It is found to have a mass of 1 kg. So its weight on the Earth is 10 N. What can you say about its mass and its weight if you take it: Calculate her weight on Mars. That is why we represent forces using arrows.

In this section, we will look at two situations where we have to think carefully about the directions of forces. The graph in Figure 3. The parachutist is accelerating or decelerating, and forces are unbalanced. If you climb to the top of a tall building, your weight will stay the same. This means that all objects fall with the same acceleration as the ball shown in Figure 3.

For many objects, the force of air resistance can affect their acceleration. Parachutists make use of air resistance. A free-fall parachutist Figure 3. At first, air resistance has little effect. However, air resistance increases as he falls, and eventually this force balances his weight. Then the parachutist stops accelerating — he falls at a steady rate known as the terminal velocity.

Opening the parachute greatly increases the area and hence the air resistance. Now there is a much bigger force upwards. The forces on the parachutist are again. Notice that his weight is constant. When air resistance equals weight, the forces are balanced and the parachutist reaches a steady speed. The parachutist is always falling velocity downwards , although his acceleration is upwards when he opens his parachute.

Find a point where the graph is sloping upwards. Going round in circles When a car turns a corner, it changes direction. Any object moving along a circular path is changing direction as it goes. A force is needed to do this. The tension in the string pulls on the apple, keeping it moving in a circle.

The lift force on its wings provides the necessary force. For an object following a circular path, the object is acted on by a force at right angles to its velocity. Studyy tip p The force that keeps an object moving in a circle always acts towards the centre of the circle. If the force disappears, the object will move off at a tangent to the circle; it will not fly outwards, away from the centre.

This alters the force provided by the engine. The bigger the force acting on the car, the bigger the acceleration it gives to the car.

Doubling the force produces twice the acceleration, three times the force produces three times the acceleration, and so on. Suppose the driver fills the boot with a lot of heavy boxes and then collects several children from college. He will notice the difference when he moves away from the traffic lights. The car will not accelerate so readily, because its mass has been increased.

Similarly, when he applies the brakes, it will not decelerate as readily as before. The mass of the car affects how easily it can be accelerated or decelerated. Drivers learn to take account of this. The greater the mass of an object, the smaller the acceleration it is given by a particular force. So, big more massive objects are harder to accelerate than small less massive ones.

If we double the mass of the object, its acceleration for a given force will be halved. We need to double the force to give it the same acceleration. This tells us what we mean by mass. It is the property of an object that resists changes in its motion. Force calculations These relationships between force, mass and acceleration can be combined into a single, very useful, equation, as shown. Examples of motion along a curved path. In each case, there is a sideways force holding the object in its circular path.

The unit of force is the newton, which is defined as shown. Worked examples 3. An Airbus A aircraft has four jet engines, each capable of providing N of thrust. What is the greatest acceleration that the aircraft can achieve? The greatest force provided by all four engines working together is: Now we have: Worked example 3.

You give the ball a large acceleration. What force is needed to give a ball of mass 0. The greatest acceleration the engines can produce is then given by: Substituting in the equation to find the force gives: How big is the force that causes this acceleration?

Using techniques, apparatus and materials Planning Observing, measuring and recording Interpreting and evaluating observations and data. If you change the force acting on an object, its acceleration changes. If you change the mass of the object, its acceleration changes. The picture shows one way to investigate this using a laboratory trolley, a light gate and a timer. The trolley is placed on a runway. A string passes over a pulley. Weights on the end of the string provide the force needed to make the trolley accelerate.

If a force of 80 N causes a box to accelerate at 0. The force F pulling the trolley is the weight of the masses m hanging from the end of the string. The mass m that is accelerating is the mass of the trolley plus the mass on the end of the string.

Decide how you will measure its acceleration. You can use a light gate and an interrupt card, or two light gates, or a motion sensor, and a data-logger and a computer. Alternatively, you could use a ticker-timer and ticker-tape. Be ready to catch it when it reaches the end of the runway. Check that you can measure its acceleration. Do not change the load on the end of the string.

Increase the mass of the trolley by placing masses on top of it. To keep the total mass constant, start with one mass on the string and nine masses on the trolley. Then, one by one, transfer masses from the trolley to the end of the string. It will make the object accelerate; it may make it change direction.

The effect of a force F depends on two things: The impulse equation sums this up: Calculate its momentum. Calculate the impulse of the force. The quantity on the left, Ft, is called the impulse of the force. So we can write the impulse equation like this:. The car is speeding up, so its momentum increases by N s. Momentum in a collision Figure 3.

The player hits the ball horizontally with a racket. How can we use the idea of momentum to describe what happens? We need to think about momentum before the racket collides with the ball, and then after the collision. The racket is moving to the right; it has momentum. The ball is stationary, so it has no momentum. The racket is moving to the right, but more slowly than before. It has lost momentum. The ball is moving rapidly to the right.

It has gained momentum. So you can see that, when the racket exerts a force on the ball, momentum is transferred from the racket to the ball. Whenever a force acts on an object, its momentum changes. At the same time, the momentum of the object causing the force also changes.

If one object gains momentum, then the other loses an equal amount of momentum. This is known as the principle of the conservation of momentum. We can state the principle in a different way. Whenever two objects interact, the total amount of momentum before they interact is the same as the total amount of momentum afterwards:. Before the collision: The next worked example shows how we can use this to work out how fast the ball in Figure 3. We can represent forces using arrows because a force has a direction as well as a magnitude.

This means that force is a vector quantity see Chapter 2. Table 3. Every vector quantity has a direction. Adding forces What happens if an object is acted on by two or more forces?

Friction opposes their pushing force. Because the forces are acting in a straight line, it is simple to calculate the resultant force, provided we take into account the directions of the forces: The car will accelerate towards the right. A firework rocket is acted on by two forces. The thrust of its burning fuel pushes it towards the right. Rules for vector addition You can add two or more forces by the following method — simply keep adding arrows end-to-end: Other vector quantities for example, two velocities can be added in this way.

Imagine that you set out to swim across a fast-flowing river. Your resultant velocity will be at an angle to the bank. Airline pilots must understand vector addition. Aircraft fly at high speed, but the air they are moving through is also moving fast. If they are to fly in a straight line towards their destination, the pilot must take account of the wind speed.

What effect will the resultant force have on the rocket? Complete the triangle by drawing an arrow from the start of the first arrow to the end of the second arrow. This arrow represents the resultant force.

Draw a scale diagram to represent these forces, as follows. In the diagram we are using a scale of 1 cm to represent 1 N. Draw a horizontal arrow, 4 cm long, to represent the 4 N force. Mark it with an arrow to show its direction. Measure the arrow, and use the scale to determine the size of the force it represents. Using the end of this arrow as the start of the next arrow, draw a vertical arrow, 3 cm long, to represent the 3 N force. Step 5: Use a protractor to measure the angle of the force.

You could also calculate this angle using trigonometry. The rocket will be given an acceleration in this direction. A head-wind blows in the opposite direction to the aircraft. Give both its speed and its direction. Read the following sentence: A force can make an object change direction, slow down, or speed up.

Copy the sentence, changing the words in italics to the correct scientific terms. An object may be acted on by several forces. What name is given to the single force that has the same effect as these forces? A force causes an object with mass to accelerate.

A car is travelling around a circular track at a steady speed. A force causes it to follow the track. Draw a diagram to illustrate your answer.

Copy the diagram and label the force arrows weight and air resistance. The two forces are equal but opposite. What is the resultant force acting on the ball? Explain why the ball falls at a steady speed. What name is given to this steady speed? He has a mass of 80 kg.

Which two? Explain your answer. Give its magnitude and direction. What acceleration is produced if the braking force is 1 N? If its mass is kg, what force must its engine provide? It pulls on each kilogram of mass with a force of 1. What will be the weight of a 50 kg mass on the Moon? The diagram shows three of the four forces acting on it.

In order to fly horizontally at a steady speed, which two of the forces shown on the aeroplane must be equal? In order to fly horizontally in a straight line, there must be a fourth force acting on the plane. Copy the diagram and draw an arrow to represent this force. The distance is km. Suggest what might have caused the return journey to be shorter. On a day when there is no wind, she runs a m race in A sketch graph not to scale showing her speed during the race is.

Keeping upright Human beings are inherently unstable. We are tall and thin and walk upright. Our feet are not rooted into the ground. So you might expect us to keep toppling over. Human children learn to stand and walk at the age of about 12 months. It takes a lot of practice to get it right. We have to learn to coordinate our muscles so that our legs, body and arms move correctly.

There is a special organ in each of our ears the semicircular canals that keeps us aware of whether we are vertical or tilting. Months of practice and many falls are needed to develop the skill of walking. We have the same experience later in life if we learn to ride a bicycle Figure 4. A bicycle is even more unstable than a person. If you ride a bicycle, you are constantly adjusting your position to maintain your stability and to remain upright.

If the bicycle tilts slightly to the left, you automatically lean slightly to the right to provide a force that tips it back again. You make these adjustments unconsciously. You know intuitively that, if you let the bicycle tilt too far, you will not be able to recover the situation, and you will end up sprawling on the ground. This cyclist must balance with great care because the load he is carrying on his head makes him even more unstable.

He must make the turning effect of his force as big as possible. How should he push? First of all, look for the pivot — the fixed point about which the door will turn. This is the hinge of the door.

To open the door, push with as big a force as possible, and as far as possible from the pivot — at the other edge of the door. That is why the door handle is fitted there. To have a big turning effect, the person must push hard at right angles to the door. Pushing at a different angle gives a smaller turning effect. The quantity that tells us the turning effect of a force about a pivot is its moment.

Her father presses down on the other end. If he can press with a force greater than her weight, the see-saw will tip to the right and she will come up in the air. Now, suppose the father presses down closer to the pivot. If he presses at half the.

Making use of turning effects Figure 4.

Balancing a beam Figure 4. Her weight causes the see-saw to tip down. Figure 4. He can increase the turning effect of his force by increasing the force, or by pushing down at a greater distance from the pivot. A see-saw is an example of a beam, a long, rigid object that is pivoted at a point.

If the beam is to be balanced, the moments of the two forces must cancel each other out.

Equilibrium When a beam is balanced, we say that it is in equilibrium. If an object is in equilibrium: Activity 4. If a resultant force acts on an object, it will start to move off in the direction of the resultant force. If there is a resultant turning effect, it will start to rotate. This always means that two or more things are balanced.

For example, place 2 N at 20 cm from the pivot. Where must you place a 1 N weight to balance this? Copy the table shown and record your results in it. Can you see a pattern? It should balance at its midpoint, as shown. You will have to move the pivot from the midpoint. Can you work out how to use this method to measure the mass of the beam? Questions 4. Which force will have the biggest turning effect? Studyy tip p If distances are given in cm, the unit of moment will be N cm. Take care not to mix these different units N m and N cm in a single calculation.

Explain why a tall tree is more likely to blow over than a short tree. We can write an equation for calculating the moment of a force, as shown. The three children in Figure 4. The weight of the child on the left is tending to turn the see-saw anticlockwise. So the weight of the child on the left has an anticlockwise moment.

The weights of the two children on the right have clockwise moments. From the data in Figure 4. We can see that, in this situation: Now let us consider the unit of moment. Since moment is a force N multiplied by a distance m , its unit is simply the newton metre N m. There is no special name for this unit in the SI system. On her own, the child on the left would make the see-saw turn anticlockwise; her weight has an anticlockwise moment.

The weight of each child on the right has a clockwise moment. Since the see-saw is balanced, the sum of the clockwise moments must equal the anticlockwise moment.

The idea that an object is balanced when clockwise and anticlockwise moments are equal is known as the principle of moments. We can use this principle to find the value of an unknown force or distance, as shown in Worked example 4. Worked example 4. It is pivoted as shown. A force of 10 N acts downwards at one end. What force F must be applied downwards at the other end to balance the beam?

Identify the clockwise and anticlockwise forces. Two forces act clockwise: One force acts anticlockwise: In equilibrium In the drawing of the three children on the see-saw Figure 4. There is also the weight of the see-saw itself, N, to consider, which also acts downwards, through its midpoint. If these were the only forces acting, they would make the see-saw accelerate downwards.

Another force acts to prevent this from happening.

There is an upward contact force where the see-saw sits on the pivot. Because the see-saw is in equilibrium, we can calculate this contact force. This force has no turning effect because it acts through the pivot. Its distance from the pivot is zero, so its moment is zero. Now we have satisfied the two conditions that must be met if an object is to be in equilibrium: You can use these two rules to solve problems concerning the forces acting on objects in equilibrium.

Studyy tip p Sometimes we know that the forces and moments acting on an object are balanced. Then we can say that it is in equilibrium. Sometimes we know the reverse, namely, that an object is in equilibrium. Then we can say that there is no resultant force on it, and no resultant moment.

So a force of 50 N is needed. You might have been able to work this out in your head, by looking at the diagram. The 20 N weight requires 20 N to balance it, and the 10 N at 1. So the total force needed is 50 N. The contact force has no moment about the pivot because it acts through the pivot. The weight of the see-saw is another force that acts through the pivot, so it also has no moment about the pivot.

Add weights to the container until the beam is balanced. You can do this by pouring in sand, or by adding small pieces of modelling clay. Was your calculation correct? Part 2 6 Weigh a 50 cm beam. Find a suitable weight similar in size to the weight of the beam and calculate where the pivot must be to balance the beam.

The weight of the beam is 40 N. Calculate the unknown force Z, and the length of the beam. Unlike a pencil, we do not topple over when touched by the slightest push. We are able to remain upright, and to walk, because we make continual adjustments to the positions of our limbs and body. We need considerable brain power to control our muscles for this. The advantage is that, with our eyes about a metre higher than if we were on all-fours, we can see much more of the world.

Circus artistes such as tightrope walkers and highwire artistes Figure 4. They use items such as poles or parasols to help them maintain their balance. The idea of moments can help us to understand why some objects are stable while others are more likely to topple over.

It could be described as top-heavy, because most of its. The two forces are in line, and the glass is in equilibrium. There is a pivot at the point where the base of the glass is in contact with the table. Its weight acts to the right of the pivot, and has a clockwise moment, which makes the glass tip right over. Centre of mass In Figure 4. Why is this? The reason is that the glass behaves as if all of its mass were concentrated at this point, known as the centre of mass.

The glass is top-heavy because its centre of mass is high up. However, rather than drawing lots of weight arrows, one for each bit of the glass, it is simpler to draw a single arrow acting through the centre of mass. Because we can think of the weight of the glass acting at this point, it is sometimes known as the centre of gravity. A person is fairly symmetrical, so their centre of mass must lie somewhere on the axis of symmetry. This is because half of their mass is on one side of the axis, and half on the other.

The centre of mass is in the middle of the body, roughly level with the navel. A ball is much more symmetrical, and its centre of mass is at its centre. For an object to be stable, it should have a low centre of mass and a wide base. The pyramid in Figure 4. The Egyptian pyramids are among the Wonders of the World. It has been suggested that, if they had been built the other way up, they would have been even greater wonders! The high-wire artiste shown in Figure 4.

A metre rule balances at its midpoint, so that is where its centre of mass must lie. The procedure for finding the centre of mass of a more irregularly shaped object is shown in Figure 4. In this case, the object is a piece of card, described as a plane lamina.

The card is suspended from a pin. If it is free to move, it hangs with its centre of mass below the point of suspension. This is because its weight pulls it round until the weight and the contact force at the pin are lined up. Then there is no moment about the pin. A plumb-line is used to mark a vertical line below the pin. The centre of mass must lie on this line. If she senses that her weight is slightly too far to the left, she can redress the balance by moving the pole to the right.

Frequent, small adjustments allow her to walk smoothly along the wire. Once the line of action of its weight is beyond the edge of the base, as in c, the glass tips right over.

There are 3 states of matter, solids, liquids and gases. Energy b. This is the most prevalent problem amongst students. You will be getting access to Biology study notes, study tips and revision tips.

Turning effect c. Experimental techniques 2. They are collected under various subheadings to help you when you revise a particular topic. Form 4 Mr. Also offers ZClass high quality past paper walkthroughs made in partnership with Cambridge Leadership College. Past papers. These notes will save you a tremendous amount of time, as they summarise the information you need to know to pass your IGCSE Biology. Thermal Physics. Conditions for equilibrium d. Here is the complete set of notes: Complete Notes.

The elements in the periodic table are ordered by what is inside their atoms. Syllabus for examination in , and But, hopefully, these notes will help you to gain the understanding required. These case studies are often used as the focus for the 7 mark questions at the end of each of the six questions. Periodic Table Worksheet Pdf Igcse. For Us. General Physics. Shawon Notes www.

Principles Of Chemistry e. Particles in solid are not free to move around. IGCSE Grade 9 Study Tips Through the principles of Chemistry, students will understand everyday life, nature and technology, and the significance of the well-being of man and the environment.

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This means that their carbon atoms are joined to each other by single bonds.