 Write down everything you know about force. Things you may want to include: ◦ Definition ◦ Formula ◦ SI Units ◦ Examples

Chapter 4

 Vectors have a magnitude and direction  Vectors can be depicted by an arrow  When drawing multiple vectors, their arrow lengths should be proportional to the vector magnitudes

1. Draw the object or a dot to represent the object. 2. Draw an arrow for each force on the object ◦ Arrows should start at the dot and point away ◦ Arrow lengths should be proportional to force magnitude. For unknown forces, estimate length 3. Label each arrow 4. Choose a direction to be positive and indicate it on the side of the diagram ◦ If object is moving, have positive direction be in direction of motion. ◦ For 2-D, show both positive directions.

 A book is sitting at rest on a table. Draw a free-body or force diagram for the book.

 A box is pushed along the floor at a constant speed. Draw a free body or force diagram for the box.

 A rope lifts a bucket at a constant speed. Draw a free body or force diagram for the bucket.

 A student is pushing against a table, but not hard enough to move it. Draw a free body or force diagram for the table.

 Power Tower is a thrill ride at Cedar Point, the roller coaster capital of the world. At the beginning of the ride, it accelerates the riders upwards. Draw a free body diagram of a rider at the beginning of a Power Tower ride.

 A canoe is sitting on frictionless ice. Two horizontal forces, 273 N and 131 N, are exerted on the canoe in the same direction. Draw a free body diagram and find the net horizontal force on the canoe.

 Now imagine the same two forces are acting in opposite directions. Draw a free body diagram and find the net horizontal force on the canoe.

 Al and Bob are playing tug-of-war (two teams pulling on a rope in opposite directions) against Chris and Dan. Al pulls with a force of 127 N, Bob pulls with a force of 93 N, Chris pulls with a force of 104 N, and Dan pulls with a force of 119 N. Draw a free-body diagram and calculate the net force on the rope.

1. An object at rest will stay at rest unless acted upon by a non-zero net force. An object in motion will stay in motion unless acted upon by a non-zero net force. 2. The acceleration of an object is equal to the net force acting on the object divided by the object’s mass. 3. For every force, there is an equal and opposite force.

 The driver of a car hits the accelerator and causes a net force of 3.00 x 10 3 N. If the car has a mass of 1.70 x 10 3 kg, what is the resulting acceleration?

 A chair is pushed horizontally with a force of 93 N, and experiences a friction force of 11 N. If the chair accelerates at 1.7 m/s 2, what is the mass of the chair?

 Free-Body Diagrams worksheet ◦ On website ◦ Due Friday  You have the rest of class to either work on the worksheet or prepare for the projectile motion test.

 A 2.5 kg rock is falling off the edge of a cliff. Gravity is pulling it down with a force of 24.5 N. There is a drag force of 7.0 N. Draw a force or free-body diagram, and solve for the acceleration of the rock.

 A skydiver with a mass of 73 kg free-falls. At one point, he has an acceleration of 8.3 m/s 2. What is the force due to air resistance at this point?

 A rope is pulling a bucket of water out of a well. The bucket of water has a total mass of 25 kg. What must the tension force be in order to accelerate the bucket at 0.60 m/s 2.

 After a few seconds of falling, the drag force on a 50.0 kg skydiver is 490 N. Draw a free- body diagram of the skydiver and calculate the acceleration of the skydiver.

 Forces are unbalanced if there is a non-zero net force.  Arrows are different lengths.  Results in an acceleration in the direction of the larger force.

 Forces Situations Worksheet ◦ On web page ◦ Due Tuesday

 A crane attached to a chain is being lowered. If the crane has a mass of 105 kg and is accelerating downward at a rate of 2.45 m/s 2, what is the tension force between the chain and crane?

 Every Halloween at Caltech, undergrads drop pumpkins (frozen by liquid nitrogen) from the top of Millikan Library, 42 meters above the sidewalk below. Ignoring air resistance, how long does it take until the pumpkin smashes into the sidewalk?

 Return to your groups  You have 15 minutes to finish  Presentations will follow ◦ Mr. Szwast will choose which member(s) of your group will present

 F g : Force of gravity; weight – down towards center of Earth  F N : Normal force – perpendicular to surface object is on (not present if object is in air)  F T : Tension – in direction of string/rope/chain  F f : Friction – opposite direction of motion or applied force  F drag : Drag – air resistance; opposite direction of motion