Lesson14.notebook July 10, 2013 Unit 2 Forces Fundamental Forces Today's goal: I can identify/name applied forces and draw appropriate free body diagrams (FBD's). There are 4 fundamental forces Gravity attraction between objects that have mass. Strong nuclear force that keeps atomic nuclei together. Weak nuclear responsible for making things radioactive. Electromagnetic combination of electrical force between particles at rest and magnetic field created when particles are moving. What is Force? Definition: The symbol for force is The units for force is Types of Force: Free Body Diagrams a vector diagram showing all the forces acting on an object helps visualize and analyze the situation called a free body diagram because it takes the object away from its surroundings
Lesson14.notebook July 10, 2013 Steps for Drawing a Free Body Diagram 1. Draw the compass points. 2. Draw a box to represent the object. Put a dot in the centre of the box 3. From that point, draw a force vector to represent each force acting on the object. Make sure to label each vector! Common Forces to Draw force due to gravity normal force force of friction Applied force Examples Draw a FBD for the following situations: 1) A car travelling with uniform velocity. 2) A car travelling with non uniform velocity. 3) A woman sleeping in a hammock. 4) A child sliding on ice.
Lesson14.notebook July 10, 2013 What is net force? Homework: page 145 # 33, 34 Handout
Lesson15.notebook July 10, 2013 Newton's First Law of Motion Today's goal: I can define/explain Newton's first and second laws and apply them to real world applications. Newton's First Law (Law of Inertia) An object at rest will continue at rest until a force is applied to it. An object which is moving will continue moving until a force is applied to it. Inertia The ability of an object to resist changing its motion. Newton's First Law in easier terms: Newton's Second Law F u = m a Any unbalanced force causes an object to accelerate. Example: What is the acceleration when an unbalanced force of 50 N [E] is applied to a 40 kg person.
Lesson15.notebook July 10, 2013 Example: A student is bowling with her friends. She gives a 7.0 kg bowling ball an acceleration of 5.0 m/s 2 [forward]. Calculate the net force on the ball. Example: A driver and his motorcycle have a combined mass of 280 kg. They accelerate from 7.0 m/s [E] to 34 m/s [E] in 4.2 seconds. What is the net force on the driver and the motorcycle? Example: Determine the missing quantities. 1) 2)
Lesson15.notebook July 10, 2013 Example: A car with mass 6500 kg has an engine driving force of 6000 N. If the car experiences a resistance force of 4500 N, determine the car's acceleration. Homework: Pg 143, #1, 4, 5, 16 Pg 144, #19 32, 35 43
Lesson16.notebook July 10, 2013 Newton's Second Law in Two Dimensions Today's goal: I can apply Newton's Second Law in two dimensions for realworld applications. The Normal Force Applied Forces and the Normal Force One Dimensional Forces Two Dimensional Forces
Lesson16.notebook July 10, 2013 Example: Determine the acceleration of the object. 20 N 37 N 21 N 30 N Example: A person of mass 70 kg is sitting on a sled. If two people are pulling her with two different ropes as shown, determine her acceleration. 50 N 40 25 60 N
Lesson16.notebook July 10, 2013 Example: Ian is pushing a lawnmower with 100 N of force down the handle. If the handle is at an angle of 40 degrees with the ground and there is a resistive force of 75 N, determine the acceleration of the 45 kg mower. Homework: Page 147, # 44, 46 51 Page 182, # 32 36
Lesson17.notebook July 10, 2013 Newton's Third Law Today's goal: I can explain Newton's Third Law and apply it to real world situations. Newton's Third Law states that Example: A cart has a chamber inside it where there is a spring that launches a ball horizontally (see diagram). If the cart is 1.2 kg, the ball is 0.07 kg and the spring exerts a 2 N force on the ball, answer the following: A) Identify 3 action reaction pairs of forces when the spring is released. B) Draw a FBD of the ball and calculate its acceleration while the spring is pushing on it.
Lesson17.notebook July 10, 2013 "Real Life" Applications: Tires: Jet Engines: Homework: Page 148 #53 55 Handout #1 7
Lesson18.notebook July 10, 2013 Frictional Forces Today's goal: I explain what a frictional force is and can draw and calculate its value using concepts learned in class. Definition: A frictional force When drawing the vector representing friction From the lab earlier this unit and the formula for friction...
Lesson18.notebook July 10, 2013 Why is F N the important force? Types of Friction
Lesson18.notebook July 10, 2013 Example: A 100 kg crate is pushed across the floor. Determine the following: A) What is the minimum force required to start moving the crate if the coefficient of static friction is 0.6? B) What is the minimum force required to continue moving the crate once it is in motion if the coefficient of kinetic friction is 0.4? C) What applied force is required to accelerate the crate at 2 m/s 2? Homework: Page 183, # 39 50
Lesson19.notebook July 10, 2013 Gravitational Fields Today's goal: I can explain the concept of "gravitational fields" and calculate the strength between two masses. Recall: Mass vs. Weight Force of Gravity in Space Force at a Distance Gravitational Fields
Lesson19.notebook July 10, 2013 Factors that affect Force due to Gravity Gravitational Field Strength
Lesson19.notebook July 10, 2013 Example: Determine the force of attraction between a 70 kg person and a 2000 kg car when they are 10 m apart. Example: A 5000 kg satellite is placed in orbit 40 000 km above the Earth's surface. If the radius of the Earth is 6400 km, determine the weight of the satellite while in orbit. Homework: Page 181 # 20 29
Lesson20.notebook July 10, 2013 Forces on an inclined Surface Today's goal: I can draw correct FBD's for an object on an inclined plane and complete the required calculations for the applied forces. The geometry: Examples: Determine all unknowns. Note: mass = 40 kg The object is stationary
Lesson20.notebook July 10, 2013 Note: mass = 50 kg The object is acceleration at 0.2 m/s 2 down the slope. Homework: Handout