Forces

Objective: TSW – Identify and describe the changes in position, direction, and speed of an object when acted upon by unbalanced forces.

How do forces work? You’d be surprised at how closely these two concepts go together. Suppose I asked you to move a heavy desk in the classroom. How would you move it? Get on one side & start pushing Grab the legs & start pulling Either way, you would be using force.

Able to change the motion of an object What is a force? A force is a push or pull Able to change the motion of an object Gravity, friction, and air resistance are three common forces on Earth Force Video

Forces There are many different forces which act on objects. If forces are balanced the object doesn’t move If forces are unbalanced the object will do one of the following things: Begin to move Stop moving Change direction Speed up Slow down

Balanced and Unbalanced Forces Forces occur in pairs and they can be either balanced or unbalanced

Force Diagrams We can show the forces acting on an object in a force diagram. In a force diagram, the force is shown with an arrow – the larger the arrow, the bigger the force The arrows in a force diagram also show the direction that the force is acting on Sometimes, the arrow will be labeled with the size of the force in Newtons (N)

Force Diagrams

Balanced Forces When two forces acting on an object are equal in size, but are opposite in direction, we say the forces are balanced. Balanced forces do not cause a change in motion.

Examples of Balances forces Forces are balanced when the net force = 0 Newtons A cell phone resting on the counter Tying an arm wrestling match A picture hanging on the wall Any object with no motion Any object moving at a constant speed

Because Gravity and Upthrust are equal the ship stays afloat. Balanced Forces The ship is floating on the water, the forces are balanced. Which forces are acting on the ship? Because Gravity and Upthrust are equal the ship stays afloat. (Water’s) Upthrust Gravity

Balanced Forces The vase is resting on the table. It is not moving, therefore the forces must be balanced. Which forces are acting on the vase? Have a look around the classroom and name some of the balanced forces in action on different objects. Gravity Table’s Upthrust

Unbalanced Forces Unbalanced forces cause a change in motion by changing the object’s speed or direction. When two forces are acting on an object and are not equal in size, we say the forces are unbalanced.

Unbalanced Forces Air resistance is pushing upwards The man and the parachute are slowly falling to the ground. Which forces are acting on the parachute? Which force is bigger? How can you tell? Gravity is the bigger force. We can tell this because the direction of movement of the man and the parachute is the same as the direction of the force of gravity. Gravity is pulling the man to the ground

Examples of Unbalanced Forces Forces are unbalanced when the net force does not equal 0 Newtons A football player tackling a quarterback Pushing a lawnmower across the yard A skydiver falling toward the ground Any object that is speeding up, slowing down, or changing direction (accelerating)

Gravity is pulling to the ground Unbalanced Forces Air resistance is pushing upwards The same forces are acting on the elephant, but without a parachute there is much less air resistance. Gravity is a much bigger force. Because there is a bigger difference between the force pulling downwards and the force pushing upwards, the elephant falls much more quickly than a man with a parachute. Gravity is pulling to the ground

Unbalanced Forces The paperclip is jumping up to the magnet. Which forces are acting on the magnet? Which is the greater force? The magnetic force is pulling the paperclip upwards The magnetic force is greater than the force of gravity therefore the paperclip moves in the direction of the biggest force. Gravity is pulling the paperclip to the ground

Forces Each team is exerting a force – what happens if the pulling force produced by each team is equal? What would happen if the team on the left were able to produce a bigger pulling force than the team on the right?

Unbalanced Forces Based on the forces shown: Which arm wrestler will likely win? Which direction will both arms move?

Which direction will the rope move? Unbalanced Forces 4 N, left 10 N, right Which direction will the rope move?

Which direction will the ball roll? Unbalanced Forces Which direction will the ball roll?

Use the textbook to define the following on your foldable Force Balanced Force Unbalanced Force Net Force Newton’s Mass Gravity Weight

Interactive Notebook Pages Use your notes to complete the Venn Diagram on balanced and unbalanced forces. Then create your balanced and unbalanced forces pockets and sort the images.

Net Force The overall force exerted on an object; measured in Newtons (N) If the net force is 0, then a change in motion will not occur If the net force is greater than 0, then a change in motion will occur 5 N + 7 N = 12 N Net Force

How to calculate net force from a picture or diagram Net Forces Net Forces How to calculate net force from a picture or diagram Subtract the forces if the arrows are pointed toward each other or pointed away from each other Add the forces together if the arrows are all pointed the same direction OR OR Practice problem(s) on checkpoint at the end.

Practice Problems 5 checkpoint questions Discuss each question with a partner Write a complete answer to each question on your notes page

Calculate the net force exerted on the box. Which direction will the box move?

Balanced or Unbalanced Forces?

Which direction will the airplane move?

Why would an object moving at a constant speed experience balanced forces?

Identify one example of balanced and unbalanced forces in the room.