Lesson summary. Grammar. Adjetives. Modals Passive voice. Present Simple. I think... In my opinion... Firstly... Secondly... Finally... To sum up...

Transcription

1 UNIT 6: FORCES AND MOTION: Lesson summary Vocabulary Grammar Content Objetives Types of forces. Mass and Weight. Motion. Speed and aceleration. Adjetives. Modals Passive voice. Present Simple. The lesson aims to help students: To know different types of forces. To understand the differences between mass and weight. To describe motion and factors about motion as speed, aceleration, position, trajectory, BRAIN STORMING What do you know about forces? What is a force? What is motion? Do you know different types of motion? I think... In my opinion... Firstly... Secondly... Finally... To sum up... Esteban Calvo Marín. FISQUIMED 1

2 Work in pairs. Answer the following questions: a) What is weight? b) How does weight differ from mass? c) What does weight depend on? d) Does a person weight more on the Earth or on the Moon? READING Forces are responsible for the actions perform everyday, for example, when we throw a ball or squash a piece of modeling clay. In these examples, applied forces cause changes to movement and deformation to objects. Force has a magnitude whose unit of measurement in the International System of Units (SI) is the newton (N). Depending on wheter the object exerting the force on another object touches it or not, there are two types of forces: contact forces and non contact forces. Gravity is a non contact force The forces exerted between two billiard balls are contact forces To measure forces we use a device called a dynamometer. Everyday forces: Motive force is what makes an object move. Friction force occurs between touching surfaces of two objects moving against each other (or an object with the air). This force always acts in the direction of an object s motion, but in the opposite orientation. Objects suspended by ropes and cables, such as a climber hanging by a rope, are subjected to tension forces. Esteban Calvo Marín. FISQUIMED 2

3 There is a force that constantly affects us all: weight. This force causes free objects to fall to the ground and keeps us glued to the Earth, if we do not exert a force to counter it. This occurs because the Earth attracts all objects, with a vertical force, towards the ground: the force of gravity. The weight (w) of a body of mass (m) is equal to the product of that mass and a magnitude known as gravity (g): w = m g On the surface of the Earth g = 9.8 m /s 2. The mass of a body is the invariable amount of matter that it has, and is measured in kilograms. Weight is the force of the Earth s attraction on that mass, and measured in newtons (N). VOCABULARY: Clay Climber Contact and non contact forces Counter Deformation Exert gravity Motive force Perform Rope Squash ACTIVITIES: 1.- Answer the following questions: a) What is the standard measurement of a force? b) What is the difference between contact and non contact forces? 2.- Are the following forces categorized as contact forces or non contact forces? The force that a magnet exerts the force used to throw a ball the force that moves bicycle pedals the force that makes a lift go up the force that make a glass fall and break Esteban Calvo Marín. FISQUIMED 3

4 3.- Give examples, with illustrations, of the following: a) Motive force b) Friction force c) Tension d) Weight 4.- Calculate the weight of the following masses: a) 5 kg; b) 60 kg; c) 400 kg. READING An object is in motion when its position changes over time. We call this a moving object. Motion is relative. It depends on the position form which we are observing it, in other words, the frame of reference. Describing motion To describe motion, we use the following terms: a) Position. This is the place the moving object occupies in relation to its origin. b) Trajectory. This is the line connecting the positions occupied by the moving object during its route. c) Distance moved. This is the length of the trajectory. d) Displacement. This is the shortest distance between the initial and final positions. The distance moved is not the same as the displacement. Esteban Calvo Marín. FISQUIMED 4

5 Types of motion The motion of an object can be classified according to the line of its trajectory. Rectilinear motion. The object moves in a straight line. Circular motion. The object moves along the circumference of a circle. Parabolic motion. The object moves in a curve under the influence of gravity. Uniform rectilinear motion. An object is in uniform rectilinear motion (URM) if its trajectory is straight (it is moving in a straight line) and its speed is constant. To calculate the distance that a moving object travels in URM, we must remember that its speed is constant. In other words, the instantaneous speed is always the same as the average speed. v = d / t d = v t VOCABULARY Average Displacement Frame of reference Gravity Instantaneous speed Motion Straight Trajectory Esteban Calvo Marín. FISQUIMED 5

6 ACTIVITIES 1.- What is a moving object? Give some examples. 2.- A cyclist moves 50 m along a straight road for 20 s. Then he goes back 20 m in 15s. Calculate: a) The total distance travelled. b) The average speed and the speed of each displacement (in m /s and km /h). 3.- Calculate the distance a runner travels in a straight line for 10 minutes at a constant speed of 18 km /h. Show the result in both metres and kilometres. 4.- Draw the x t and v t graphs of a moving object travelling at a constant speed of 12 m /s along a straight road, with the starting position at x = 26 m. What will its position be after 1 minute? Esteban Calvo Marín. FISQUIMED 6

7 LISTENING a) How can t you move a rock? b) What is a force? c) What is gravity? Esteban Calvo Marín. FISQUIMED 7