1. Aim: How do we explain Newton’s first two laws of motion?

2. Newton’s 2nd Law
∑F = ma The net force acting on an object is the vector sum of all forces acting on an object. It is also called the resultant force. The net force acting on an object is equal to the mass of the object multiplied by the acceleration of the object.

3. Force as a Vector
Forces are vectors so we add forces like vectors.

4. Thought Question 1
Two horizontal forces, F1 =(3N)i-(4N)j and F2 =-(1N)i-(2N)j
pull a banana slit across a frictionless lunch counter. Without using a calculator, determine which of the vectors in the freebody diagram best represent
F1 and b)F2
What is the net-force component along c) the x axis and d) the y axis?
Into which quadrants do e) the net force vector and f) the split’s acceleration vector point?

5. Thought Question 1 5 7 2N
-6N
Quadrant 4

6. Thought Question 2
The figure below shows overhead views of four situations in which forces act on a block that lies on a frictionless floor. If the force magnitudes are chosen properly, in which situations is it possible that the block is (a) stationary and (b) moving with a constant velocity?
2 and 4

7. Thought Question 3
In the figure below, two forces F1 and F2 act on a “Rocky and Bullwinkle” lunch box as the lunch box slides at constant velocity over a frictionless lunchroom floor. We are to decreases the angle ᶱ of F1 without changing the magnitude of F1. To keep the lunch box sliding at constant velocity, should we increase, decrease, or maintain the magnitude of F2?
The magnitude of F2 must be increased

8. Thought Question 4
The freebody diagrams for four situations in which an object is pulled by several forces across a frictionless floor. In which situations does the object’s acceleration a have a) an x component and b) a y component? c) In each situation, give the direction of a by naming either a quadrant or a direction along an axis. (No calculations)
2,3 and 4
1,3,and 4
Y-axis for 1
X-axis for 2
Quadrant 4 for 3
Quadrant 3 for 3

9. Problem 1
A 0.30 kg hockey puck slides on the horizontal frictionless surface of an ice rink. It is struck simultaneously by two different hockey sticks. The two constant forces that act on the puck as a result of the hockey sticks are parallel to the ice surface and are shown in the pictorial representation shown. The force F1 has a magnitude of 5.0 N and F2 has a magnitude of 8.0 N. Determine the acceleration of the puck while it is in contact with the two sticks.

10. Problem 1
34 m/s^2 at 30 degree angle

12. Problem 1 Cont
Determine the components of a third force that when applied to the puck along with the two causes the puck to have zero acceleration. Since the net force is (8.7i+5.23j)N, a force of (-8.7 i -5.23j) N is required to cancel this out
-8.7N=x, -5.2N=y