above the horizontal from the ball. Set the individual vectors and press GO to hit the center of each target in turn.
The target to the left is at a 150° angle. It is the “extra credit” target. Determining the correct ratio of vectors will require a little thought. We
allow for rounding with this target; if you set one of the vectors to 10 N, you can solve the problem by setting the other one to the appropriate
closest integer value.
5.26 - Gotchas
An object has a speed of 20 km/h.It swerves to the left but maintains the same speed.Was a force involved? Yes. A change in speed or
direction is acceleration, and acceleration requires a force.
An object is moving.A net force must be acting on it. No. Only if the object is accelerating (changing speed or direction) is there a net force.
Constant velocity means there is no net force.
No acceleration means no forces are present. Close. No acceleration means no net forces. There can be a balanced set of forces and no
acceleration.
“I weigh 70 kilograms.” False. Kilograms measure mass, not weight.
“I weigh the same on Jupiter as I do on Mars.” Not unless you dieted (lost mass) as you traveled from Jupiter to Mars. Weight is gravitational
force, and Mars exerts less gravitational force.
“My mass is the same on Jupiter and Mars.” Yes.
The normal force is the response force to gravity. This is too specific of a definition. The normal force appears any time two objects are brought
in contact. It is not limited to gravity. For instance, if you lean against a wall, the force of the wall on you is a normal force. If you stand on the
ground, the normal force of the ground is a response force to gravity.
“I push against a wall with a force of five newtons. The wall pushes back with the same force.” Close, but it is better to say, “The same amount
(magnitude) of force but in the opposite direction.”
“I pull on the Earth with the same amount of gravitational force that the Earth exerts on me.”True. You are an action-reaction pair.