1. Forces and Newton’s Laws

2. Force A Force is a push or a pull that one body exerts on another.
All Forces are measured in Newtons (N)

3. Balanced Forces
Force that are equal in opposite directions and act on an object to produce a net force of zero.
20N
Net force = 0
20N
Balanced Forces cause no change in motion

4. Unbalanced Forces
Forces acting on an object to produce a net force that is positive.
20N
Net force = 5N
Box moves to the right
15N
Unbalanced Forces cause a change in motion.

5. Some Types of Forces
Friction is the force between two objects that opposes the motions of either object.
Example: Rubbing your hands together.

6. Some Types of Forces
Air Resistance is the force that acts on objects as they move through air.
The amount of air resistance acting on an object depends on two factors:
1) Speed (Velocity). The faster an object moves, the more air resistance acts on it
More air resistance Less air resistance
2) Surface area. The larger the surface area of an object the more air resistance acts in it.
Crumpled paper
Flat paper
Less air resistance More air resistance

7. Some Types of Forces
Gravity is the force that holds everything in the universe together.
“Every object in the universe exerts the force of gravity on all other objects.”
Gravity depends on two factors:
1) Distance. The shorter the distance between two objects the greater the force of gravity between them
More Gravity
Less Gravity
2) Mass. The greater the mass of an object, the more gravity it exerts on other objects.
More Gravity
Less Gravity

8. Some Types of Forces
Weight is a force. It is the force that gravity exerts on an object due to the object’s mass.
“Like all forces weight is measured in Newtons.”
Weight depends on two factors: Weight = MassxGravity
1) Mass. The more mass an object has, the more gravity acts on it and the more weight it has.
10kg
5kg
More Weight 5N
Less Weight 2.5 N

9. weight = mass x acceleration of gravity
Some Types of Forces
weight = mass x acceleration of gravity
W = mg W m g

10. Some Types of Forces Jupiter Earth Less Weight 2.5 N More Weight 5N
2) The amount of Gravity on the planetary body the object is on.
Jupiter
Earth
10kg
10kg
Less Weight 2.5 N
More Weight 5N

11. Sir Isaac Newton

12. Newton’s First Law It is often called the Law of Inertia.
Newton’s First Law states, “An object at rest will remain at rest unless acted upon by an unbalanced force while an object in motion will remain in motion with constant speed and
direction unless acted upon by an unbalanced force”
It is often called the Law of Inertia.

13. What is inertia?
An object’s tendency to resist a change in it’s motion.
This means that an object:
Will be hard to move if it is at rest
Example: The plates on a set table.
Or a tomato being shot.

14. NO…why? Would the bowling ball and the golf ball have the same
inertia?
NO…why?
The more massive an object is, the greater its
inertia…
And the greater an objects inertia is, the greater
the force required to put the object in motion

15. Examples of Inertia
Will be hard to slow an object down or speed it up if it is moving
Example People involved in a car stopping suddenly fly forwards because they keep moving at the same speed as the car.
Only the seatbelt stops them.

16. Newton’s Second Law of Motion
Newton’s Second Law states, “When a net force acts on an object the object will accelerate in the direction of the net force”.
The greater the mass (of the object being accelerated) the greater
the amount of force needed (to accelerate the object).
Everyone knows that heavier objects require more force to move the same distance as lighter objects

17. Newton’s Second Law of Motion
Newton’s Second Law gives us an exact relationship between
force, mass, and acceleration.
It Sates that the amount of force needed to move an object is equal to it’s mass multiplied by its acceleration
FORCE = MASS times ACCELERATION

18. Example of how Newton's Second Law works
Mike's car, which weighs 1,000 kg, is out of gas.
Mike is trying to push the car to a gas station,
and he makes the car go 0.05 m/s/s. How much force is Mike using? F M A
Answer = 50 newtons

19. Newton’s Third Law of Motion
Newton’s Third Law states, “For every action there is an equal and opposite re-action”
What does this mean?
This means that for every force there is a reaction force that is equal in
size, but opposite in direction.
That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.

20. Newton’s Third Law of Motion
Explains how a rocket works
The rocket's action is to push down on the ground
with the force of its powerful engines, and the reaction
is that the ground pushes the rocket upwards with an equal force.

21. Quiz 1) Who was the scientist who gave us the Laws of Motion?
2 What is another name for the first law of motion?
3) Which law explains why we need to wear seatbelts?
4) Which law says that force is equal to mass times acceleration (F=MA)?