Newton's Third Law
According to Newton’s third law of motion, forces always act in __________ and _________pairs
Equal and Opposite
Forces always occur in pairs, what does this mean?
One body cannot exert a force on another without experiencing a force itself.
Newton's Second Law is F= m*a
Solve for Mass
m = F/a
Newton's Second Law is F= m*a
Solve for acceleration
a= F/m
What does a Vector Quantity mean?
a quantity that has both force and direction
When one object exerts a force on another object, the second object exerts _______________ force on the first object
Equal and opposite
The forces exerted by two objects on each other are often called
an action reaction force pair
Vehicle 1 has a Mass = 1,500 kg and an acceleration of 150 m/s2. Apply Newton’s Second Law of Motion to determine the force exerted by the vehicle on the wall during the crash.
F= m*a
1,500 kg * 150 m/s2
225,000 N
If you are given the initial velocity and time of a vehicle as well as its final velocity and time, how do you find acceleration?
V(final) - V(initial)/ T(final) - T(initial)
If the forces acting on the object are balanced, the object will remain at rest or stay in motion with constant velocity. What will happen if the forces acting on an object are unbalanced?
the object will accelerate in the direction of the net force.
Is the following an example of Newton's Third Law?
Imagine you’re driving a bumper car and are about to bump a friend in another car. When the two cars collide, your car pushes on the other car. That car pushes on your car with the same force, but in the opposite direction.
Yes, equal and opposite forces acting on different objects
Identify action and reaction forces (action-reaction pairs): Earth’s gravity pulls down on you
1. Force of Earth on Human =FEH
2. Force of Human on Earth = FHE
Vehicle 2 has a Mass = 1,500 kg and an acceleration of -40 m/s2. Apply Newton’s Second Law of Motion to determine the force exerted by the vehicle on the wall during the crash.
F=m*a
1,500 kg * -40 m/s2
60,000 N
Vehicle 2 has a Mass = 1,500 kg and a Velocity = 20 m/s. Calculate the acceleration of the vehicle as its velocity changes from 20 to 0 m/s in 0.5 seconds
a= V(final) - V(initial)/ T(final) - T(initial)
V(final) - V(initial)/ T(final) - T(initial)
0-20/.5-0 = -20/.5= -40 m/s2
Identify action and reaction forces (action-reaction pairs): You pat your friend on the back with your hand
Your hand pats your friend on the back FHB
Your friend's back pushes back on your hand FBH
When action and reaction forces are exerted by two objects, the accelerations of the objects depend on the ____________ of the objects. This is because of Newton's ___________ Law of motion which is _____________
Masses
Second
F=m*a
For the following interaction, identify action and reaction forces (action-reaction pairs):
A helicopter blade pushes air downward.
A helicopter blade pushes air downward = F HA
The air pushes up on the helicopter with an equal but opposite force = FAH
Vehicle 3 has a Mass = 2,000 kg and an acceleration of 1,500 m/s2. Apply Newton’s Second Law of Motion to determine the force exerted by the vehicle on the wall during the crash.
F=m*a
F= m*a
2000 kg * 1,500 m/s2
3,000,000 N
Vehicle 1 has a Mass = 1,500 kg and a Velocity = 15 m/s. Calculate the acceleration of the vehicle as its velocity changes from 15 to 0 m/s in 0.1 seconds.
a= (V(final) - V(initial))/ (T(final) - T(initial))
V(final) - V(initial)/ T(final) - T(initial)
0-15/.1-0 = -15/.1= -150 m/s2
A vehicle crashes into a wall with 20,000 N of force. Apply Newton’s Third Law of Motion to determine the force exerted by the wall on the vehicle.
20,000 N
If according to Newton’s Third Law of Motion, every force has an equal and opposite force, then does it mean that every force in the universe cancels? Explain
Action and reaction force pairs don’t always cancel because they act on different objects. Forces can cancel only if they act on the same object
Explain why the normal force and the force of gravity acting on a book as it sits on a desk are not Newton’s Third Law of Motion force pairs
The force acting on the table is due to gravity (is this the same as a gravitational force?), and the forcing acting from the table to the book is a reaction force. So one is a gravitational, and the other is not. Therefore this is not Newton's Third Law as the forces must be of the same type
A person standing in a canoe exerts a force of 700 N to throw an anchor over the side. Find the acceleration of the canoe if the total mass of the canoe and the person is 100 kg
a= F/m
a= 700 N /100 kg = 7 m/s2
Vehicle 3 has a Mass = 2,000 kg and a Velocity = 15 m/s. Calculate the acceleration of the vehicle as its velocity changes from 15 to 0 m/s in 0.01 seconds.
a= (V(final) - V(initial))/ (T(final) - T(initial))
V(final) - V(initial)/ T(final) - T(initial)
0-15/.01-0 = -15/.01= -1,500 m/s2
When a Bus and a Car run into each other, which vehicle hits the other with more force? Explain.
Neither would enact a greater force on the other. The force on the bus and car are the same. This is Newton's Third Law. Any action has an equal and opposite reaction.
Let's assume the bus and the car are moving at the same speed. This means the bus has more momentum ( mass * velocity) than the car because it has more mass than the car. So the car will feel the impact more since it has less momentum and have higher damage