Download 1 Chapter 4: Forces and the Laws of Motion pages 119 144 Date __

Chapter 4: Forces and the Laws of Motion pages 119 ­ 144 Date _____
A force is an action exerted on a object which may change the object's state of rest or motion.
Forces can cause objects to In each case the force is responsible for a change in velocity with respect to time which is
___________________________________.
Forces can act through contact or at a distance.
Field forces Contact Forces
1
The SI unit of force is newton (N).
When a force acts on a 1 kg mass and accelerates it 1 m/s2, 1 newton of force has been applied. One average apple or the meat in a quarter pounder weigh about 1 newton.
When you push on a toy car, it accelerates. If you push harder, the acceleration is greater. The acceleration of the car depends in the force's magnitude. The direction the car moves depends in the force's direction.
Force is a __________ quantity.
Since more than one force may act on an object, the vector sum of all the forces acting on the object is
the net force. Since force is a vector quantity both the ____________
and the ____________ of the net force are important.
2
Force Diagrams
Free­body diagrams are diagrams to show the relative magnitude and direction of all forces acting on an object.
The size of the arrow reflects the __________________ of the force and the direction of the arrow shows the ________________ which the force is acting.
The object is represented by a box and the force arrow is drawn from the box outward in the direction in which the force is acting.
Fapp is the force which is applied to an object.
Ffrict is the force exerted by an surface as the object moves across it or makes an effort to move across it.
Fgrav or Fg is the force of gravity on an object also known as its weight
Fnorm is the support force exerted on an object when it is in contact with another stable object.
3
Forces in the same direction add.
Forces in the opposite direction subtract.
The net force is the vector sum of all
the forces acting on an object.
Ftens is the tension force transmitted through a string or rope when it is pulled tight.
Fair is the air resistance force which is a frictional force as an object moves through the air
4
Below are four free­body diagrams. For each situation, determine the net force acting on the object.
5
Balanced Forces: When the net force on an object is ZERO, the object experiences a balanced force and there is NO CHANGE in motion. The object is in equilibrium.
Does an object have to be at rest to be in equilibrium? Why or why not?
Unbalanced Forces: When the net force on an
object is NOT ZERO, the object experiences
an unbalanced force and the object
accelerates.
6
Balanced or Unbalanced Forces?
The object below is moving at a constant velocity to the right when the following forces are applied. Does it experience a balanced or unbalanced force?
5N
5N
What is the affect of the forces on the motion of the object?
The object below is moving at a constant velocity to the left when the following forces are applied. Does it experience a balanced or unbalanced force?
3N
4N
What is the affect of the forces on the motion of the object?
7
Mass versus Weight
Mass is
Weight is
The weight of an object can be calculated using
The weight of an object depends on its ____________.
8