How to create document, Exams of Computer science

Download How to create document and more Exams Computer science in PDF only on Docsity!

FORCE

SECTION

General Science Year 1

VIGOUR BEHIND LIFE

Forces acting on substances and mechanisms

INTRODUCTION

Hello learners! You will recall from your science lessons in Junior High School that a force is a push or pull that can change the state of motion or the shape of an object.

In this section, you will identify and explain more concepts associated with forces like velocity, acceleration, and speed. We will also discuss other forces like friction, tension, and gravitational forces.

At the end of this section, you will be able to:

Identify and explain concepts associated with forces

KEY IDEA

Force is a vector quantity, which means it has both magnitude (size) and direction. It is measured in Newtons (N). Forces are a fundamental concept in physics that describes interactions between objects and can cause changes in their motion or shape.

IDENTIFICATION AND EXPLANATION OF

CONCEPTS ASSOCIATED WITH FORCES

Forces play a vital role in our everyday lives in situations such as kicking a soccer ball, running and weeding the school farm, and many other less easily identifiable scenarios.

Frictional Forces

1. Frictional forces can be described as forces that arise when two objects physically touch each other. 2. Friction resists relative motion between two surfaces in contact.

In groups, perform the following experiment and share your observations.

Activity 6.2: Exploring the effects of different surfaces and the frictional forces they generate.

Aim: To investigate the effects of friction on the distance an object can slide along a surface Materials:

• Wooden block / a book / a toy car
• Smooth surface (e.g., a glass table, a plastic tray)
• Rough surface (e.g., sandpaper, a carpet, floor)
• Ruler or measuring tape
• Weighing scale (optional)

Procedure:

1. Start by placing the smooth surface (e.g., glass table) on a flat, stable table or floor. 2. Take the wooden block (or the object with a flat surface) and place it on a smooth surface. 3. Gently push the block with a constant force and measure the distance it travels before coming to a stop. 4. Mark the block’s motion’s starting and ending points. 5. Record the distance in a table. 6. Repeat the above steps, ensuring the pushing force is the same, for the rough surface (e.g., A-4 size sandpaper) and record the distance the block travels before stopping. 7. Analyse the results, including an analysis of the challenges involved with ensuring a constant pushing force and suggestions about how to improve the consistency of this. 8. Compare the distance the block travelled on the smooth surface with the distance it travelled on the rough surface. See Annex 6.

Activity 6.3: Advantages and disadvantages of frictional forces in everyday life.

Discuss with your friends more benefits and detriments of friction and write them down.

Gravitational Force

Observe the image in Figure 6.2 and consider the forces acting on the ball as it moves through the sky.

Fig. 6.2: Ball throwing

The gravitational force is the force of attraction between any two objects with mass. It is this same force that is responsible for keeping planets in orbit around stars and objects anchored to the Earth’s surface as shown in Figure 6.3.

Fig. 6.3: Gravitational force holding the planets in their respective orbits

Now do the following activity to investigate more on gravitational force.

Displacement is the distance travelled in a particular direction.

Velocity is measured in units such as metres per second (m/s) or kilometres per hour (km/h).

Positive velocity indicates motion in the forward direction, while negative velocity indicates motion in the reverse direction.

Activity 6.5: Exploring velocity

In a small group, complete the following activity. Aim: Investigate the concept of velocity and how it relates to everyday life. Materials: Stopwatch, measuring tape, toy cars, markers, chart paper, plank of wood/ramp. Procedure

1. Using a measuring tape, mark out a one-metre length on your plank of wood or ramp. 2. Lift one end of the ramp by placing it onto a stable object, such as a book. 3. Set your stopwatch and the toy car in motion at the top of the one-metre distance. Stop the stopwatch when your toy car has travelled one metre. 4. Calculate the velocity of the toy car. 5. Repeat the experiment, but this time with the ramp lifted to a greater height (by using more books!). 6. Record all of your results in a table. 7. Describe how distance and time affect velocity.

In the next discussion, observe the images in Figures 6.4 and 6.5.

Fig. 6.4: 100m race Fig. 6.5: 3,000m race

In observing the images in Figures 6.4 and 6.5, identify:

a. Which of the races will you say covers long distances and which one has a short distance coverage? b. Which one will require a shorter time to finish? c. Which one will require a longer time to finish? d. Which race is likely to involve greater accelerations? e. Discuss your responses with the friend next to you.

Now go through the discussions below on distance and speed and compare them to your responses.

Distance

Distance is a scalar quantity representing the total path length an object covers during its motion. It measures the total amount of ground covered, regardless of the direction taken. Distance is always positive or zero, as it only considers the magnitude of motion. It is measured in units such as metres (m), kilometres (km), miles (mi), etc.

Speed

Speed describes how fast an object is moving. Speed is a scalar quantity representing the rate of change of distance with respect to time. It only considers the magnitude of motion and does not consider the direction. The formula for calculating speed is:

speed = _____________distance travelled time taken

Speed is measured in units like metres per second (m/s), kilometres per hour (km/h), or miles per hour (mph). Unlike velocity, speed does not involve direction and can only be positive or zero.

Acceleration

Let us discuss acceleration and compare it to velocity

a. When something is accelerating, its velocity is changing. b. Acceleration = change in velocity/ time taken a = _____(v – u) t

Activity 7: Experiment about acceleration (gravity) - Investigate the concept of acceleration using simple materials.

Materials: Toy car or small object that can roll e.g. iron ball, car tyre etc., smooth flat surface (such as a tabletop or floor), measuring tape or ruler, stopwatch or timer, notebook and pen. Procedure:

1. Set up the smooth, flat surface for the experiment. Ensure there is enough distance for the toy car to accelerate down the ramp and then come to a stop. 2. Set the toy car at one end of the surface and indicate its starting point. 3. Mark uniform distances along the surface with a measuring tape or ruler (e.g. 10cm intervals). 4. Start the stopwatch when you release the toy car/rolling item from its starting place. 5. Measure the time it takes for the toy car/rolling item to reach each marked spot on the surface. You may find it easiest to do this by filming the car in slow motion using your phone, with the stopwatch in the shot. 6. To calculate the average speed of the toy car/rolling item between intervals, use the formula speed = distance/time. 7. Analyse speed data to determine if the toy car is accelerating, decelerating, or at a constant pace. 8. To compute acceleration, apply the formula: acceleration = (final velocity - initial velocity) / time. 9. Repeat the experiment and make adjustments to see how surface smoothness and incline affect acceleration. 10. Document your observations, measurements, and conclusions in the notebook.

Cohesive and Adhesive Forces

During your basic school education, you learn that cohesive forces are the attractive forces between molecules of the same substance that make them stick together. For example, the forces between individual water molecules are cohesive. Adhesive forces are the attractions between different substances that help them stick together; an example is water adhering or sticking to a glass surface.

Now do the activities below to determine the differences and share your findings with the class.

Activity 6.8: Understanding Cohesive and Adhesive Forces

This activity can be done in your science group. Aim: To differentiate between cohesive and adhesive forces through a series of interactive experiments. Experiment 1: Cohesive Forces Materials: Small containers (e.g. cut-out plastic bottle) or cups, water, salt, spoon, small objects (e.g., paper clips, coins), droppers/pipettes, and paper towels.

1. Pick 2 containers and label them A and B. 2. Fill the 2 small containers with water. 3. Stir a pinch of salt into container A until dissolved. 4. Using a pipette, drop water from each container onto a clean, flat surface and compare the behaviour of plain water in B and saltwater droplets in A. 5. Explain how saltwater’s cohesive forces hold droplets together compared to ordinary water.

This force can be observed in experiments like dropping water onto a penny, where cohesion and surface tension allow multiple drops to accumulate before spilling over. Saltwater has lower cohesion than plain water, affecting the number of drops that can stay on the penny. Experiment 2: Adhesive Forces Materials:

• Capillary tubes (for example thin
• Plain-coloured straw for drinking fizzy drinks
• Borosilicate glass tubes)
• Tissue strip
• Water
• Food colouring (optional)

Activity 6.9: Real-life applications of force

Having discussed some examples of forces, go through the following real-life applications and add on in the third column with more examples. Table 6.1: Real-life applications of force

Type of force in action

Everyday activity Add on (give more examples of everyday activities)

Friction Gripping, writing Pushing/pulling Opening doors

Gravity Orbiting planets, falling objects Capillarity Drinking Fanta with a straw

Activity 10: Sum it all up

Produce a summary sheet or poster on the topic of forces and motion. Include a glossary of key terms and highlight the differences between distance and displacement, speed and velocity, and acceleration. Include examples from your everyday life, or from areas/hobbies that interest you, to illustrate your work.

ANNEX 6.1 – SOLUTIONS TO SOME

ACTIVITIES

Activity 6.

You will notice that the block travelled a shorter distance on the rough surface than on the smooth surface. In the experiment, the rough surface created more friction between the block and the surface, which caused it to slow down and stop sooner.

Activity 6.

Objects of any mass accelerate at the same rate when free-falling on Earth. This means that all objects will hit the ground at the same time when released from the same height, as long as there are no other forces acting to increase or decrease their velocity (such as air resistance).

Activity 6.

When the ramp is lifted to a greater height, the car takes a shorter amount of time to descend the one-metre distance. A smaller time gives a greater velocity (as time is the denominator in the velocity formula).

Activity 6.

1. Velocity = Distance_______ Time

= _____200 m 20 s Velocity = 10 m/s The average velocity of the runner is 10 metres per second.

2. Given: Distance = 300 kilometres, Time = 5 hours Velocity = Distance_______ Time = 300 kilometres / 5 hours = 60 km/h

REVIEW QUESTION

Review Questions 6.

1. During a soccer match, a player kicks the ball with a force of 50 N. If the ball has a mass of 0.5 kg. a. What will be its acceleration immediately after being kicked? b. What external forces should you consider, that could affect the ball’s motion afterward? 2. You are stranded on a deserted road, and your car is stuck in the mud. a. What factors might be preventing the car from moving? b. How can you get the car moving? 3. In what ways does the gravitational force affect the motion of planets, moons, and the Sun, in our Solar System? 4. How do adhesive and cohesive forces interact with gravity and other forces to influence the behaviour of fluids in different scenarios, such as in a falling droplet or during liquid movement through a porous medium?

REFERENCES

1. General Science Curriculum for Senior High Schools
2. Smith, J., & Johnson, M. (2021). Teaching Forces: Strategies for Engaging Students in Physics Concepts. Journal of Science Education, 15(2), 45-56.
3. Brown, A., & Williams, R. (2019). Interactive Approaches to Teaching Forces in Middle School Science. Journal of STEM Education, 8(3), 112-
   1. Oxford University Press. Complete Physics for Cambridge IGCSE, Third Edition.
4. Blanchet, L. (2006). Gravitational radiation from post-Newtonian sources and inspiralling compact binaries. Living Rev. Relativity 9.
5. Blanchet, L., and Faye, G. (2000). Hadamard regularization. Math. Phys. 41, 7675–7714.
6. Kennefick, D. 2005. Einstein versus the Physical Review. Physics Today 58(9), 43–48.
7. Kennefick, D. 2007. Traveling at the Speed of Thought: Einstein and the Quest for Gravitational Waves. Princeton University Press.

GLOSSARY

Celestial body: any natural object located in space. An object in space that has physical substance, distinguishes them from phenomena such as light or radiation.