Force, Mass, and Acceleration

Student Success Statements:

• 8.6C - investigate and describe applications of Newton's three laws of motion such as in vehicle restraints, sports activities, amusement park rides, Earth's tectonic activities and rocket launches

Students will be able to:

• Understand Newton’s Second Law – the relationship between force and acceleration

• Apply Newton’s law in a laboratory situation where the relationship between force, mass and acceleration are being explored

What is Newton’s law of force and acceleration?

• Known as Newton’s 2nd law of motion, it states that - the acceleration of an object depends on the mass of the object and the net force applied

• Recall that mass is how much matter is in an object (which is related to density)

• And that net force is the total force acting on an object

• Acceleration is the rate at which velocity changes over time.

Newton’s Second Law:

• Acceleration is produced when a force acts on an object.

• The greater the mass of the object being accelerated, the greater the amount of force needed to accelerate the object.

• The Second Law gives us an exact relationship between force, mass, and acceleration

• The Second Law has 2 parts – let’s look at them

Newton’s Second Law – Part 1• Acceleration Depends on Mass

• Look at the two carts below. Which one will require the smallest amount of force to push?

• You would only have to exert a small force on the empty cart to accelerate it. However, when the cart is full, the same amount of force will not accelerate the cart as much as before.

Explaining the relationship: The acceleration of an object decreaseswith increased mass of that object

• Look at this situation:

Newton’s Second Law – Part 2

• Acceleration Depends on Force

• The carts below have boxes with the same mass on them. If we apply different amounts of force, which one will have the greater acceleration?

Explaining the relationship: The acceleration of an object increases with increased force

• When moving a same sized box:

• Small force on the box means a small acceleration, but a larger push (force) means the box will accelerate faster and further

Newton’s Second Law – Part 2

• In your notes summarize the relationship between force and acceleration of objects that have the same mass. Use the picture to guide you.

More on Acceleration -

• Recall from a previous lesson – that we use

• Acceleration can be calculated be rearranging the equation so that

a = F/m

Remember, Acceleration -

•Acceleration occurs when the motion of

an object changes.

• Acceleration happens when an object

does any 1 or more of these:

Speeds up

Slows down

Changes direction

The force of Gravity

• Gravity is the force of attraction that exists between any two objects that have mass.

• The force of gravity depends on 2 factors:

• 1. the mass of the objects

• 2. the distance between them.

Gravity is known as a “constant”

• It applies to all objects the same

• On earth, it has a constant value of 9.8 m/s²

• Pictured next are two balls that have different masses. If they are released at the same time, which one will land first?

Rate of Gravity• What is the difference between the two? Which

one will land first?

Working towards Understanding:

• The balls landed at the same time. Why is this?

Find the acceleration of the first ball :

If a = F/m

You were given force and mass values -

F = 10 kg*m/s2

m = 1 kg

Find the acceleration of the first ball :

Find the acceleration of the second ball :

Again, a = F/m

Find the acceleration of the second ball :

So, even though their masses are different, the acceleration is the same.

Results:• When the only force acting on a falling object is

gravity, the object is said to be in free fall. An object in free fall accelerates as it falls because gravity acts as an unbalanced force and causes the object to accelerate.

Sports and F = ma

Wrap up video:

Lab Page: Force and Acceleration Lab

Lab Expectations and Instructions:

• Lab Behavior: Be Principled and safe

• Lab Instructions: Follow the procedure as written, if you have questions, ask before doing!

• What to complete at home: the graph and analysis questions. Graph can be worked on in class if your group completes the lab and cleans up first

Lab Clean Up:• Place supplies back in the same order that you

found them

• Leave it tidy so that the next group can be ready to start on time – just like YOU did.

• Straighten the room, chairs pushed in, any trash thrown away