1. Section 1
Forces

2. What is force? A force is a push or a pull. Some examples are -
Catching a baseball and hitting a baseball
Forces cause an object to change its speed, direction or both.
Gravity, magnetism, friction, and applied force are example of types of basic forces called fundamental forces.
©Lawrence Manning/Corbis

3. How are force and motion related?
A force can cause the motion of an object to change.
Example – Soccer, When you strike the ball with your foot, it causes the ball to stop and change direction.
Example – Pool , The force of the moving pool ball causes the ball at rest to move in the direction of the force.

4. How is the net force on an object determined?
The sum of all the force acting on an object. Forces have a direction like displacement and velocity .
Forces are measured in the SI unit of Newtons (N).
Rules for combining – add forces in the same direction, subtract forces in opposite directions, if they are not in the same or opposite directions, they cannot be directly added together.
10 N
7 N
10 N
5 N
10 N
3 N

5. Unbalanced Forces
The net force causes the object to move one way or the other.
It can be from opposite directions or the same direction.
Unbalanced forces are forces acting on an object from opposite directions that are not equal.
These objects with unbalanced forces acting upon them are in MOTION - MOVING.

6. Balanced Forces The net force on the object is zero.
There is no change in motion.

7. Balanced Forces
Balanced forces are forces acting on an object from opposite directions that are equal.
These objects with balanced forces acting upon them will most likely be STILL – Not Moving

8. Why is there friction between objects?
Friction is the force that opposes the sliding motion of two surfaces that are touching each other.
Suppose you give a skateboard a push with your hand. After you let go, the skateboard slows down and eventually stops.
Because the skateboard’s motion is changing as it slows down, there must be a force acting on it. The force that slows the skateboard is called friction.

9. Friction
Friction
A force that works against motion; the action of one surface or object rubbing against another surface or object.
Friction stops or slows down moving objects.
Friction can help moving objects change direction.
Types of friction
Static – prevents two surfaces from sliding past each other because of the microwelds that have formed between the bottom of the object and the surface. EX. Pushing a box across the floor.
Sliding - opposes the motion of the two surfaces as it slides the microwelds are constantly breaking and forming as the objects slide past each other.
Rolling – Static friction between the wheel and the surface where they touch. Wheels would not work without this friction. Friction is the traction of tires.

10. Gravity The attractive force which acts on all objects with mass.
Gravity is an attractive force between any two objects that depends on the masses of the objects and the distance between them.
One of the basic forces.
Is a long range force.
Is sometimes discussed as a field because objects don’t have to touch. All objects are surrounded by a gravitational field.

11. Gravity
Law of Universal Gravitation is the relationship between the gravitational force between two objects, the objects’ masses, and the distance between them. G = 6.67 x 10 -¹¹ m³/kg x s²
Explains why you feel the Earth’s gravity but not the sun’s or your pencil’s. The sun is too far away and the pencil’s mass is too small to feel their attractions.

12. What is the difference between mass and weight?
Weight is the gravitational force exerted on an object.
Mass is the amount of matter in an object.
g is the gravitational strength.
Weight and mass are not the same. Weight is a force.

14. Assessment 2.
What is the gravitational force exerted on an object called?
centripetal force A
friction B
momentum C
weight D
CORRECT

15. Assessment 3.
Which term best describes the forces on an object with a net force of zero?
balanced forces A
CORRECT
unbalanced forces B
inertia C
acceleration D

16. Assessment 4.
Which body exerts the strongest gravitational force on you?
the Moon A
Earth B
CORRECT
the Sun C
this book D

17. Assessment 5.
The graph shows the speed of a car moving in a straight line. Over which segments are the forces on the car balanced?
A and C A
B and D B
CORRECT
C and E C
A, C, and E D

18. Assessment 6. Which of the following is not a force? weight frictionB
momentum C
CORRECT
air resistance D