Forces Rule 1: Draw the diagram (make it simple). Rule 2: The force arrow starts at the centre of the object being acted on. Rule 3: Always check the units!!!!!!!!!!!!! Newton’s 3 Laws of Motion Newton’s 1st Law: An object will remain in a constant state of motion unless acted upon by a resultant force. Newton’s 2nd Law: The acceleration of an object is directly proportional to the magnitude of the resultant force acting upon it, and inversely proportional to the object’s own mass. Newton’s 3rd Law: If body A exerts a force on body B, then body B will exert a force of the same size and type, but in the opposite direction, on body A. Write your own version of each of these laws in simple language, because if you can explain it simply it shows you really understand it Newton’s 1st Law means: _________________________________________________________________ _________________________________________________________________ Newton’s 2nd Law means: _________________________________________________________________ _________________________________________________________________ _________________________________________________________________ Newton’s 3rd Law means: _________________________________________________________________ _________________________________________________________________ _________________________________________________________________ Air Resistance Weight Friction Upthrust A) B) C) ` D) D) E) F) Stationary G) Faster Constant Speed Slower Stationary Constant Speed Which way will each of these boxes move and why? (A) (B) (C) Box A will move to the left because ----Box B will move diagonally---Box C will move diagonally 9 N beats 4N and both 3 N cancel out--up to the left because both—down to the left because -9N’s beat the 3N and 4N-----7 and 9 beats 3 Add arrows next to each of these photos showing how the sizes of the friction and forwards force compare to each other. Draw the arrow representing friction in blue and the arrow representing the forwards force in red. Are the forces balanced or unbalanced in each case? Speeding up Still/stopped Slowing down In speeding up the forces are unbalanced with the forward force being greater. In still/stopped the forces are balanced. In slowing down the forces are unequal with friction being greater. 20 0 1000 100 0 20000 Why do objects float? Objects float because the upthrust and gravity are equal Circle the correct definition of density: The amount of space an object takes up. How heavy an object is for its size. Mass per unit Volume The width and solidity of an object. How wide and hard it is The weight of an object. Calculate the densities of blocks A-D. Remember! You must calculate the volume of each block first: (A) (B) 14g (C) 24g (D) 16g A) Volume: 1*1*1=1 Density: 14 B) Volume: 2*2*2=8 Density: 3 C) Volume: 3*3*3=27 Density:0.59 D) Volume: 4*4*4=64 Density:0.54 35g Newton’s Second Law, as it is stated at the start is talking about acceleration. It says that if you double the resultant force on the object you double the acceleration of the object and if you double the mass of the object you make it twice as hard to push so you halve its acceleration. Therefore the equation is F=M*A 𝒂= 𝑭 𝑚 so 𝑭 =? & 𝑚 =? M=F/A Use these equations to answer the following questions. 1 2 3 4 5 6 7 Easy What is the unit of force? Newton Write the equation needed to calculate force if the mass and acceleration is known. F=M/A Rearrange the force equation to calculate mass. M=F/A Rearrange the force equation to calculate acceleration. A=F/M What is the force if the mass is 20 kg and the acceleration 80 m/s/s? 1600 N What is the force if the mass is 50 kg and the acceleration is 900 m/s/s/? Medium What is the force if the mass is 3.5 kg and the acceleration is 80 m/s/s? What is the force if the mass is 800 kg and the acceleration is 60 m/s/s? Hard What is the force of a ball with a mass of 5 kg if it accelerates at 10 m/s/s? What is the force on a man if he accelerates at 42 m/s/s and has a mass of 112 kg? What is the acceleration if the mass is 80 kg and the force 75 N? What is the mass if the force is 90 N and the acceleration is 80 m/s/s? What is the mass if the force is 20 N and the acceleration is 80 m/s/s? What is the acceleration of a cat if it has a mass of 8 kg and hits the cat flap with a force of 65 N? What is the mass of a dog if it accelerates at 20 m/s/s and has a force of 8 N? Draw a car moving forward on a road. What are the forces acting upon the car? Draw arrows to show them. What are the forces acting upon a box being pushed by a man? Draw arrows to show the forces. What is the acceleration if the force is 50 N and the mass is 100 kg? 2 What is the acceleration if the force is 74 N and the mass is 655 kg? 8.85 What is the force if the mass is 40 kg and the acceleration is 23 m/s/s?