Force and Motion Notes

Sir Isaac Newton (1643 – 1727)

One of the world’s greatest scientists

Developed the 3 Laws of Motion

What is a Force?

A force is a push or pull

When one object pushes or pulls another object, the first object is exerting a force on the second object

Forces are described by strength and direction

And are drawn with arrows

Forces are measured in Newtons

SI unit of force

Symbol: N

Measured by using a spring scale

There are two types of forces

Balanced Forces(No change in motion)

No Acceleration!

Unbalanced Forces

(Change in Motion)

Acceleration!

Net Force

We calculate forces using net force.

The overall force on an object after all the forces acting on it are added is called the net force.

Net Force = 3N

Balanced Forces and Motion

Are equal forces acting on one object in opposite directions.

Equal forces acting on an object will not change the object’s motion.

The net force is 0 (zero).

Net force = 0 (push)

Net force = 0 (pull)

Balanced Forces

There is no change in motion

Unbalanced Forces and Motion

Can cause an object to: start moving

stop moving

change direction or speed.

When two forces act in the same direction, they add together.

When forces act in opposite directions you subtract the forces. If one force is greater than the other force, the overall force is

in the direction of the greater force.

Unbalanced Forces

The forces acting on an object are not equal

When a net force greater than 0 acts on an object

the forces are UNBALANCED. One or more force is stronger than others

Change in Motion occurs

How to calculate net force

Once again - the net force is the overall force or total amount of force acting on an object (a combination of the magnitude and direction)

For example, in this tug of war, the net force is 3N to the left

5N 2N

The forces are

in opposite

directions.

Subtract the

numbers.

More examples of net force calculations

Two people are trying to push away a box full of rotting eggs, who ends up with the box?

If there are two people trying to get this box full of money, who ends up with it?

Sam

10N

Omar

15N

Lauren

20N

Olivia

30N

Calculation Practice

225 N

Unbalanced

Unbalanced

13 N

Balanced

0 N

=

Bill Nye

Let’s examine the Spring Scale more closely

Definition: A spring scale is a tool used to measure force.

It works in the same way the rubber band does. The spring inside it stretches based on the amount of force added to it.

Use will use a spring scale in the lab today

Simple Machines and Forces

Lever Pulley Wheel and Axle

WedgeScrewInclined Plane

So…what is a simple machine and what makes them so simple ?

A simple machine has few or no moving parts.

They often use only the force (effort) of a person to do the work.

Simple machines make our effort easier.

Why are they so important??

Simple machines are important because they can make a physical job easier by changing the magnitude (amount of work) or the direction of the force exerted to do work.

The amount of force output is greater than the size of the force you put in.

Force and Motion Lab

EXPLORATORY STATIONS

Journal

In table of contents “Forces Lab”

On the next clean page, write for the title “Forces Lab”

Station 1 - Ball

1. Place the ball on the counter, where the “X” is.

2. Write in your journal: Is this an example of balanced or unbalanced force? Why?

3. GENTLY bounce the ball so that it bounces up from the floor to your hand.

4. Draw the movement in your journal and label the direction of forces.

5. Write in your journal: Is this movement an example of balanced or unbalanced force? Why?

Station 2 - Dominoes

1. Set up the dominoes in a row so that they will touch each other when they fall.

2. Write in your journal: What type of force is going to make the dominoes fall?

3. Knock the dominoes over.

4. Draw your domino set up in your journal and draw arrows to show the direction of movement.

Station 4 – Spring Scale

One person holds the spring scale while another person puts weights on the scale.

Write these down in your journal:

1. What does the spring scale measure?

2. Write down the Force in Newtons (N) for each weight.

Weight: Force (N):

1. 100g

2. 200g

3. 500g

Station 5 – Force Problems

Work these problems –

1. Draw the boxes and arrows, including the forces in Newtons.

2. Show your math work!

Station 6 – Tug of War!

View the picture and then sketch it in your journal:

Tabitha and Zach are playing tug-of-war. If Zach pulls the rope to the right with a force of 800N and Tabitha pulls the rope to the left with a force of 800N, what will happen to the flag in the middle of the rope?

Write this sentence and fill in the blanks: “The flag will _________ because __________________________________ .

Tabitha Zach