Forces
The Definition of force
Define Friction
What is the force that results when surfaces of object rub against each other and oppose motion
Definition of Inertia
What is the tendency of an object to resist changes in its velocity
In order to start sliding a refrigerator across the floor, a man must exert an enormous amount of this kind of friction
What is static
The unit for force
What is a newton (N)
Define Kinetic friction and give an example
What is friction that opposes motion once the motion has already started. Also sliding friction
Newtons First Law
What is an object in motion (or at rest) will stay in motion (or at rest) until it is acted upon by an outside force
Once the refrigerator has started moving what kind of friction is this
What is kinetic friction
The total net force
What is the total overall force acting on an object (after all the forces are combined)
Define Static Friction
Newtons Second Law
What is when an object is acted on by one or more unbalanced forces, the net force is equal to the mass of the object times the resulting acceleration.
A child is pushing her toy cross the room at a constant velocity to the east. IF the static friction between this toy and the floor is 15 N, while the kinetic friction is 10 N, child exerting what force
10 N west
Since the object is moving at a constant velocity we know the object acceleration is zero. Since the total force exerted on an object is equal to the objects mass times its acceleration (Newtons 2nd law) then the total force on the object is zero as well. This means that the child exerts enough for to counteract kinetic friction but no more. You know we are talking about kinetic friction bc the toy is already moving.
Forces are balanced
When the net force is zero and there is no change in the objects motion
Static friction can exert a force of up to 700 N on a 500 kg box of bricks. The kinetic frictional force is only 220 N. How many newtons of force must a worker exert to get the box moving?
What is more than 700 N.
If the static frictional force is 700 N, the worker must apply more than 700 N of force to get the box moving.
Newtons Third Law
What is for every action there is an equal and opposite reaction
A man leans up against a wall with a force of 20 N to the east. The force entered by the wall on the man is
What is 20 N west
A father is trying to teach his child to ice skate. As the child stands still, the father pushes him forward with an acceleration of 2.0 m/s2 north. If the childs mass is 20 kg, what is the force with which the father is pushing? Remember F= m X a
What is 40 N north