Newton's First Law (2.3)

• Natuurkunde
• Middelbare school
• vwo
• Leerjaar 3

Paragraph 2.3

Newtons First Law

True or False, and explain;
When you stop cycling on your bycicle you slow down because there are no more forces.

Newton's First Law

"When the resulting force is equal to 0, an object moves with a constant speed or is standing stil. "

Constant Speed

As long as the resulting force is equal to 0 then the speed will remain the same: 21,4 m/s

When you are cycling the muscle force is equal to the resistance. When this occurs the forces are in equilibrium.

Acceleration

When there is a resulting force on an object the object will accelerate, decelerate or change direction. 

You can see that the velocity wil keep increasing as result when a person uses more muscle force. 

When he stops excerting this force only the friction remains and the object will slow down.

So..

When the resulting force is 0 the velocity remains the same. 

When the resulting force is more than 0 the velocity increases.

When the resulting force is less than 0 the velocity decreases. 

State at what times in the graph there is an acceleration, deceleration and a uniform motion.

Driving forces and resisting forces

There are resisting forces 

- Air friction

- Sliding resistance

- Rolling resistance

And driving forces

- Force of gravity

- Engine Force

- Muscle Force

Resulting Force Fres = Fdriving - Fresisiting

Reducing friction

Air resistance

- Streamlining

- Decrease the frontal area

Sliding resistance

- The mass of the object

- The 'smoothness'of the surfaces of the objects.

Rolling friction

- Harder/Flatter underground.

- Pressure of the tires

Which kinds or resistance do you experience when you are cycling?

1. Air resistance
2. Sliding resistance
3. Rollinf friction
4. All of them

A rain drop falls down with a constant velocity. On the raindrop the force of gravity is applied and air resistance (Fr,a). Which of the statements is true?

1. Fg= Fr,a
2. Fg > Fr,a
3. Fg < Fr,a
4. Fr,a increases

A truck accelerates (with a constant engine force) from 72 to 90 km/h. The resulting force:

1. remains the same
2. increases
3. Decreases
4. is 0

What happens to a box if the man stops pushing and the sliding resistance is gone (ignore the air resistance)?

1. The box will slow down until it comes to a complete stop
2. The box will keep sliding forever.
3. You can't say