F=ma and vector directions

[G1SG2]

From F=ma, we can see that acceleration is always in the direction of the net force, since m is positive. However, if we have a car that's slowing down/decelerating (moving in the positive x direction), we can see that the acceleration vector is point backwards, in the negative x direction since the car is decelerating and is slowing down. However, won't the friction force be pointing forward, as it always does for a car (opposing the backward movement of the care tires)? Or am I wrong? Because if that's how the diagram would look like,then it would seem that force and acceleration are pointing it opposite directions, which would not make sense as per F=ma. Any clarification would be appreciated, thanks.

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[Doodl3s]

the force of friction always points in the direction opposite movement. this is one of those intuitive thinking questions. When a car tries to slow down and stop short, the tires skid forward. SO the force of friction is point BACK on the tires of a car slowing down because inertia wants the car to keep going forward, so when you slow down you need friction force to push back on the tires.

Normally the tires have to push the car forward so they use the friction going in the same direction. Tires essentially pull on the ground using static frictional force. To stop, they pull on the ground again, but in the other direction

 

[G1SG2]

the force of friction always points in the direction opposite movement. this is one of those intuitive thinking questions. When a car tries to slow down and stop short, the tires skid forward. SO the force of friction is point BACK on the tires of a car slowing down because inertia wants the car to keep going forward, so when you slow down you need friction force to push back on the tires.

Normally the tires have to push the car forward so they use the friction going in the same direction. Tires essentially pull on the ground using static frictional force. To stop, they pull on the ground again, but in the other direction

Okay, got it, thanks.

Also, I have a question regarding uniform circular motion. Acceleration and velocity are constant in magnitude, BUT since BOTH vectors are constantly changing direction, we can say that in uniform circular motion, acceleration and velocity are not constant, right?

 

[sv3]

Okay, got it, thanks.

Also, I have a question regarding uniform circular motion. Acceleration and velocity are constant in magnitude, BUT since BOTH vectors are constantly changing direction, we can say that in uniform circular motion, acceleration and velocity are not constant, right?

correct. it is called uniform b/c speed is constant.